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| |
| \begin_body |
| |
| \begin_layout Title |
| The Speex Manual |
| \begin_inset Newline newline |
| \end_inset |
| |
| Version 1.2 |
| \end_layout |
| |
| \begin_layout Author |
| Jean-Marc Valin |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
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| \begin_layout Standard |
| Copyright |
| \begin_inset ERT |
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| \begin_layout Plain Layout |
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| \backslash |
| copyright |
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| 2002-2008 Jean-Marc Valin/Xiph.org Foundation |
| \end_layout |
| |
| \begin_layout Standard |
| Permission is granted to copy, distribute and/or modify this document under |
| the terms of the GNU Free Documentation License, Version 1.1 or any later |
| version published by the Free Software Foundation; with no Invariant Section, |
| with no Front-Cover Texts, and with no Back-Cover. |
| A copy of the license is included in the section entitled "GNU Free Documentati |
| on License". |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
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| \begin_inset CommandInset toc |
| LatexCommand tableofcontents |
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| \begin_inset Newpage newpage |
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| \begin_inset Newpage newpage |
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| \end_layout |
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| \begin_layout Chapter |
| Introduction to Speex |
| \end_layout |
| |
| \begin_layout Standard |
| The Speex codec ( |
| \family typewriter |
| http://www.speex.org/ |
| \family default |
| ) exists because there is a need for a speech codec that is open-source |
| and free from software patent royalties. |
| These are essential conditions for being usable in any open-source software. |
| In essence, Speex is to speech what Vorbis is to audio/music. |
| Unlike many other speech codecs, Speex is not designed for mobile phones |
| but rather for packet networks and voice over IP (VoIP) applications. |
| File-based compression is of course also supported. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The Speex codec is designed to be very flexible and support a wide range |
| of speech quality and bit-rate. |
| Support for very good quality speech also means that Speex can encode wideband |
| speech (16 kHz sampling rate) in addition to narrowband speech (telephone |
| quality, 8 kHz sampling rate). |
| \end_layout |
| |
| \begin_layout Standard |
| Designing for VoIP instead of mobile phones means that Speex is robust to |
| lost packets, but not to corrupted ones. |
| This is based on the assumption that in VoIP, packets either arrive unaltered |
| or don't arrive at all. |
| Because Speex is targeted at a wide range of devices, it has modest (adjustable |
| ) complexity and a small memory footprint. |
| \end_layout |
| |
| \begin_layout Standard |
| All the design goals led to the choice of CELP |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| CELP |
| \end_layout |
| |
| \end_inset |
| |
| as the encoding technique. |
| One of the main reasons is that CELP has long proved that it could work |
| reliably and scale well to both low bit-rates (e.g. |
| DoD CELP @ 4.8 kbps) and high bit-rates (e.g. |
| G.728 @ 16 kbps). |
| |
| \end_layout |
| |
| \begin_layout Section |
| Getting help |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Getting-help" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| As for many open source projects, there are many ways to get help with Speex. |
| These include: |
| \end_layout |
| |
| \begin_layout Itemize |
| This manual |
| \end_layout |
| |
| \begin_layout Itemize |
| Other documentation on the Speex website (http://www.speex.org/) |
| \end_layout |
| |
| \begin_layout Itemize |
| Mailing list: Discuss any Speex-related topic on speex-dev@xiph.org (not |
| just for developers) |
| \end_layout |
| |
| \begin_layout Itemize |
| IRC: The main channel is #speex on irc.freenode.net. |
| Note that due to time differences, it may take a while to get someone, |
| so please be patient. |
| \end_layout |
| |
| \begin_layout Itemize |
| Email the author privately at jean-marc.valin@usherbrooke.ca |
| \series bold |
| only |
| \series default |
| for private/delicate topics you do not wish to discuss publicly. |
| \end_layout |
| |
| \begin_layout Standard |
| Before asking for help (mailing list or IRC), |
| \series bold |
| it is important to first read this manual |
| \series default |
| (OK, so if you made it here it's already a good sign). |
| It is generally considered rude to ask on a mailing list about topics that |
| are clearly detailed in the documentation. |
| On the other hand, it's perfectly OK (and encouraged) to ask for clarifications |
| about something covered in the manual. |
| This manual does not (yet) cover everything about Speex, so everyone is |
| encouraged to ask questions, send comments, feature requests, or just let |
| us know how Speex is being used. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Here are some additional guidelines related to the mailing list. |
| Before reporting bugs in Speex to the list, it is strongly recommended |
| (if possible) to first test whether these bugs can be reproduced using |
| the speexenc and speexdec (see Section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Command-line-encoder/decoder" |
| |
| \end_inset |
| |
| ) command-line utilities. |
| Bugs reported based on 3rd party code are both harder to find and far too |
| often caused by errors that have nothing to do with Speex. |
| |
| \end_layout |
| |
| \begin_layout Section |
| About this document |
| \end_layout |
| |
| \begin_layout Standard |
| This document is divided in the following way. |
| Section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Feature-description" |
| |
| \end_inset |
| |
| describes the different Speex features and defines many basic terms that |
| are used throughout this manual. |
| Section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Command-line-encoder/decoder" |
| |
| \end_inset |
| |
| documents the standard command-line tools provided in the Speex distribution. |
| Section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Programming-with-Speex" |
| |
| \end_inset |
| |
| includes detailed instructions about programming using the libspeex |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| libspeex |
| \end_layout |
| |
| \end_inset |
| |
| API. |
| Section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Formats-and-standards" |
| |
| \end_inset |
| |
| has some information related to Speex and standards. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The three last sections describe the algorithms used in Speex. |
| These sections require signal processing knowledge, but are not required |
| for merely using Speex. |
| They are intended for people who want to understand how Speex really works |
| and/or want to do research based on Speex. |
| Section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Introduction-to-CELP" |
| |
| \end_inset |
| |
| explains the general idea behind CELP, while sections |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Speex-narrowband-mode" |
| |
| \end_inset |
| |
| and |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Speex-wideband-mode" |
| |
| \end_inset |
| |
| are specific to Speex. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Codec description |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Feature-description" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| This section describes Speex and its features into more details. |
| \end_layout |
| |
| \begin_layout Section |
| Concepts |
| \end_layout |
| |
| \begin_layout Standard |
| Before introducing all the Speex features, here are some concepts in speech |
| coding that help better understand the rest of the manual. |
| Although some are general concepts in speech/audio processing, others are |
| specific to Speex. |
| \end_layout |
| |
| \begin_layout Subsection* |
| Sampling rate |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| sampling rate |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The sampling rate expressed in Hertz (Hz) is the number of samples taken |
| from a signal per second. |
| For a sampling rate of |
| \begin_inset Formula $F_{s}$ |
| \end_inset |
| |
| kHz, the highest frequency that can be represented is equal to |
| \begin_inset Formula $F_{s}/2$ |
| \end_inset |
| |
| kHz ( |
| \begin_inset Formula $F_{s}/2$ |
| \end_inset |
| |
| is known as the Nyquist frequency). |
| This is a fundamental property in signal processing and is described by |
| the sampling theorem. |
| Speex is mainly designed for three different sampling rates: 8 kHz, 16 |
| kHz, and 32 kHz. |
| These are respectively referred to as narrowband |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| narrowband |
| \end_layout |
| |
| \end_inset |
| |
| , wideband |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| wideband |
| \end_layout |
| |
| \end_inset |
| |
| and ultra-wideband |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| ultra-wideband |
| \end_layout |
| |
| \end_inset |
| |
| . |
| |
| \end_layout |
| |
| \begin_layout Subsection* |
| Bit-rate |
| \end_layout |
| |
| \begin_layout Standard |
| When encoding a speech signal, the bit-rate is defined as the number of |
| bits per unit of time required to encode the speech. |
| It is measured in |
| \emph on |
| bits per second |
| \emph default |
| (bps), or generally |
| \emph on |
| kilobits per second |
| \emph default |
| . |
| It is important to make the distinction between |
| \emph on |
| kilo |
| \series bold |
| bits |
| \series default |
| \emph default |
| |
| \emph on |
| per second |
| \emph default |
| (k |
| \series bold |
| b |
| \series default |
| ps) and |
| \emph on |
| kilo |
| \series bold |
| bytes |
| \series default |
| \emph default |
| |
| \emph on |
| per second |
| \emph default |
| (k |
| \series bold |
| B |
| \series default |
| ps). |
| \end_layout |
| |
| \begin_layout Subsection* |
| Quality |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| quality |
| \end_layout |
| |
| \end_inset |
| |
| (variable) |
| \end_layout |
| |
| \begin_layout Standard |
| Speex is a lossy codec, which means that it achieves compression at the |
| expense of fidelity of the input speech signal. |
| Unlike some other speech codecs, it is possible to control the trade-off |
| made between quality and bit-rate. |
| The Speex encoding process is controlled most of the time by a quality |
| parameter that ranges from 0 to 10. |
| In constant bit-rate |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| constant bit-rate |
| \end_layout |
| |
| \end_inset |
| |
| (CBR) operation, the quality parameter is an integer, while for variable |
| bit-rate (VBR), the parameter is a float. |
| |
| \end_layout |
| |
| \begin_layout Subsection* |
| Complexity |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| complexity |
| \end_layout |
| |
| \end_inset |
| |
| (variable) |
| \end_layout |
| |
| \begin_layout Standard |
| With Speex, it is possible to vary the complexity allowed for the encoder. |
| This is done by controlling how the search is performed with an integer |
| ranging from 1 to 10 in a way that's similar to the -1 to -9 options to |
| |
| \emph on |
| gzip |
| \emph default |
| and |
| \emph on |
| bzip2 |
| \emph default |
| compression utilities. |
| For normal use, the noise level at complexity 1 is between 1 and 2 dB higher |
| than at complexity 10, but the CPU requirements for complexity 10 is about |
| 5 times higher than for complexity 1. |
| In practice, the best trade-off is between complexity 2 and 4, though higher |
| settings are often useful when encoding non-speech sounds like DTMF |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| DTMF |
| \end_layout |
| |
| \end_inset |
| |
| tones. |
| \end_layout |
| |
| \begin_layout Subsection* |
| Variable Bit-Rate |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| variable bit-rate |
| \end_layout |
| |
| \end_inset |
| |
| (VBR) |
| \end_layout |
| |
| \begin_layout Standard |
| Variable bit-rate (VBR) allows a codec to change its bit-rate dynamically |
| to adapt to the |
| \begin_inset Quotes eld |
| \end_inset |
| |
| difficulty |
| \begin_inset Quotes erd |
| \end_inset |
| |
| of the audio being encoded. |
| In the example of Speex, sounds like vowels and high-energy transients |
| require a higher bit-rate to achieve good quality, while fricatives (e.g. |
| s,f sounds) can be coded adequately with less bits. |
| For this reason, VBR can achieve lower bit-rate for the same quality, or |
| a better quality for a certain bit-rate. |
| Despite its advantages, VBR has two main drawbacks: first, by only specifying |
| quality, there's no guaranty about the final average bit-rate. |
| Second, for some real-time applications like voice over IP (VoIP), what |
| counts is the maximum bit-rate, which must be low enough for the communication |
| channel. |
| \end_layout |
| |
| \begin_layout Subsection* |
| Average Bit-Rate |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| average bit-rate |
| \end_layout |
| |
| \end_inset |
| |
| (ABR) |
| \end_layout |
| |
| \begin_layout Standard |
| Average bit-rate solves one of the problems of VBR, as it dynamically adjusts |
| VBR quality in order to meet a specific target bit-rate. |
| Because the quality/bit-rate is adjusted in real-time (open-loop), the |
| global quality will be slightly lower than that obtained by encoding in |
| VBR with exactly the right quality setting to meet the target average bit-rate. |
| \end_layout |
| |
| \begin_layout Subsection* |
| Voice Activity Detection |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| voice activity detection |
| \end_layout |
| |
| \end_inset |
| |
| (VAD) |
| \end_layout |
| |
| \begin_layout Standard |
| When enabled, voice activity detection detects whether the audio being encoded |
| is speech or silence/background noise. |
| VAD is always implicitly activated when encoding in VBR, so the option |
| is only useful in non-VBR operation. |
| In this case, Speex detects non-speech periods and encode them with just |
| enough bits to reproduce the background noise. |
| This is called |
| \begin_inset Quotes eld |
| \end_inset |
| |
| comfort noise generation |
| \begin_inset Quotes erd |
| \end_inset |
| |
| (CNG). |
| \end_layout |
| |
| \begin_layout Subsection* |
| Discontinuous Transmission |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| discontinuous transmission |
| \end_layout |
| |
| \end_inset |
| |
| (DTX) |
| \end_layout |
| |
| \begin_layout Standard |
| Discontinuous transmission is an addition to VAD/VBR operation, that allows |
| to stop transmitting completely when the background noise is stationary. |
| In file-based operation, since we cannot just stop writing to the file, |
| only 5 bits are used for such frames (corresponding to 250 bps). |
| \end_layout |
| |
| \begin_layout Subsection* |
| Perceptual enhancement |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| perceptual enhancement |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Perceptual enhancement is a part of the decoder which, when turned on, attempts |
| to reduce the perception of the noise/distortion produced by the encoding/decod |
| ing process. |
| In most cases, perceptual enhancement brings the sound further from the |
| original |
| \emph on |
| objectively |
| \emph default |
| (e.g. |
| considering only SNR), but in the end it still |
| \emph on |
| sounds |
| \emph default |
| better (subjective improvement). |
| \end_layout |
| |
| \begin_layout Subsection* |
| Latency and algorithmic delay |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| algorithmic delay |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Every speech codec introduces a delay in the transmission. |
| For Speex, this delay is equal to the frame size, plus some amount of |
| \begin_inset Quotes eld |
| \end_inset |
| |
| look-ahead |
| \begin_inset Quotes erd |
| \end_inset |
| |
| required to process each frame. |
| In narrowband operation (8 kHz), the delay is 30 ms, while for wideband |
| (16 kHz), the delay is 34 ms. |
| These values don't account for the CPU time it takes to encode or decode |
| the frames. |
| \end_layout |
| |
| \begin_layout Section |
| Codec |
| \end_layout |
| |
| \begin_layout Standard |
| The main characteristics of Speex can be summarized as follows: |
| \end_layout |
| |
| \begin_layout Itemize |
| Free software/open-source |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| open-source |
| \end_layout |
| |
| \end_inset |
| |
| , patent |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| patent |
| \end_layout |
| |
| \end_inset |
| |
| and royalty-free |
| \end_layout |
| |
| \begin_layout Itemize |
| Integration of narrowband |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| narrowband |
| \end_layout |
| |
| \end_inset |
| |
| and wideband |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| wideband |
| \end_layout |
| |
| \end_inset |
| |
| using an embedded bit-stream |
| \end_layout |
| |
| \begin_layout Itemize |
| Wide range of bit-rates available (from 2.15 kbps to 44 kbps) |
| \end_layout |
| |
| \begin_layout Itemize |
| Dynamic bit-rate switching (AMR) and Variable Bit-Rate |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| variable bit-rate |
| \end_layout |
| |
| \end_inset |
| |
| (VBR) operation |
| \end_layout |
| |
| \begin_layout Itemize |
| Voice Activity Detection |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| voice activity detection |
| \end_layout |
| |
| \end_inset |
| |
| (VAD, integrated with VBR) and discontinuous transmission (DTX) |
| \end_layout |
| |
| \begin_layout Itemize |
| Variable complexity |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| complexity |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Itemize |
| Embedded wideband structure (scalable sampling rate) |
| \end_layout |
| |
| \begin_layout Itemize |
| Ultra-wideband sampling rate at 32 kHz |
| \end_layout |
| |
| \begin_layout Itemize |
| Intensity stereo encoding option |
| \end_layout |
| |
| \begin_layout Itemize |
| Fixed-point implementation |
| \end_layout |
| |
| \begin_layout Section |
| Preprocessor |
| \end_layout |
| |
| \begin_layout Standard |
| This part refers to the preprocessor module introduced in the 1.1.x branch. |
| The preprocessor is designed to be used on the audio |
| \emph on |
| before |
| \emph default |
| running the encoder. |
| The preprocessor provides three main functionalities: |
| \end_layout |
| |
| \begin_layout Itemize |
| noise suppression |
| \end_layout |
| |
| \begin_layout Itemize |
| automatic gain control (AGC) |
| \end_layout |
| |
| \begin_layout Itemize |
| voice activity detection (VAD) |
| \end_layout |
| |
| \begin_layout Standard |
| The denoiser can be used to reduce the amount of background noise present |
| in the input signal. |
| This provides higher quality speech whether or not the denoised signal |
| is encoded with Speex (or at all). |
| However, when using the denoised signal with the codec, there is an additional |
| benefit. |
| Speech codecs in general (Speex included) tend to perform poorly on noisy |
| input, which tends to amplify the noise. |
| The denoiser greatly reduces this effect. |
| \end_layout |
| |
| \begin_layout Standard |
| Automatic gain control (AGC) is a feature that deals with the fact that |
| the recording volume may vary by a large amount between different setups. |
| The AGC provides a way to adjust a signal to a reference volume. |
| This is useful for voice over IP because it removes the need for manual |
| adjustment of the microphone gain. |
| A secondary advantage is that by setting the microphone gain to a conservative |
| (low) level, it is easier to avoid clipping. |
| \end_layout |
| |
| \begin_layout Standard |
| The voice activity detector (VAD) provided by the preprocessor is more advanced |
| than the one directly provided in the codec. |
| |
| \end_layout |
| |
| \begin_layout Section |
| Adaptive Jitter Buffer |
| \end_layout |
| |
| \begin_layout Standard |
| When transmitting voice (or any content for that matter) over UDP or RTP, |
| packet may be lost, arrive with different delay, or even out of order. |
| The purpose of a jitter buffer is to reorder packets and buffer them long |
| enough (but no longer than necessary) so they can be sent to be decoded. |
| |
| \end_layout |
| |
| \begin_layout Section |
| Acoustic Echo Canceller |
| \end_layout |
| |
| \begin_layout Standard |
| In any hands-free communication system (Fig. |
| |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "fig:Acoustic-echo-model" |
| |
| \end_inset |
| |
| ), speech from the remote end is played in the local loudspeaker, propagates |
| in the room and is captured by the microphone. |
| If the audio captured from the microphone is sent directly to the remote |
| end, then the remote user hears an echo of his voice. |
| An acoustic echo canceller is designed to remove the acoustic echo before |
| it is sent to the remote end. |
| It is important to understand that the echo canceller is meant to improve |
| the quality on the |
| \series bold |
| remote |
| \series default |
| end. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float figure |
| wide false |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Graphics |
| filename echo_path.eps |
| width 10cm |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Acoustic echo model |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "fig:Acoustic-echo-model" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Section |
| Resampler |
| \end_layout |
| |
| \begin_layout Standard |
| In some cases, it may be useful to convert audio from one sampling rate |
| to another. |
| There are many reasons for that. |
| It can be for mixing streams that have different sampling rates, for supporting |
| sampling rates that the soundcard doesn't support, for transcoding, etc. |
| That's why there is now a resampler that is part of the Speex project. |
| This resampler can be used to convert between any two arbitrary rates (the |
| ratio must only be a rational number) and there is control over the quality/com |
| plexity tradeoff. |
| \end_layout |
| |
| \begin_layout Section |
| Integration |
| \end_layout |
| |
| \begin_layout Standard |
| Knowing |
| \emph on |
| how |
| \emph default |
| to use each of the components is not that useful unless we know |
| \emph on |
| where |
| \emph default |
| to use them. |
| Figure |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "fig:Integration-VoIP" |
| |
| \end_inset |
| |
| shows where each of the components would be used in a typical VoIP client. |
| Components in dotted lines are optional, though they may be very useful |
| in some circumstances. |
| There are several important things to note from there. |
| The AEC must be placed as close as possible to the playback and capture. |
| Only the resampling may be closer. |
| Also, it is very important to use the same clock for both mic capture and |
| speaker/headphones playback. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float figure |
| wide false |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Graphics |
| filename components.eps |
| width 80text% |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Integration of all the components in a VoIP client. |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "fig:Integration-VoIP" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Compiling and Porting |
| \end_layout |
| |
| \begin_layout Standard |
| Compiling Speex under UNIX/Linux or any other platform supported by autoconf |
| (e.g. |
| Win32/cygwin) is as easy as typing: |
| \end_layout |
| |
| \begin_layout LyX-Code |
| % ./configure [options] |
| \end_layout |
| |
| \begin_layout LyX-Code |
| % make |
| \end_layout |
| |
| \begin_layout LyX-Code |
| % make install |
| \end_layout |
| |
| \begin_layout Standard |
| The options supported by the Speex configure script are: |
| \end_layout |
| |
| \begin_layout Description |
| --prefix=<path> Specifies the base path for installing Speex (e.g. |
| /usr) |
| \end_layout |
| |
| \begin_layout Description |
| --enable-shared/--disable-shared Whether to compile shared libraries |
| \end_layout |
| |
| \begin_layout Description |
| --enable-static/--disable-static Whether to compile static libraries |
| \end_layout |
| |
| \begin_layout Description |
| --disable-wideband Disable the wideband part of Speex (typically to save |
| space) |
| \end_layout |
| |
| \begin_layout Description |
| --enable-valgrind Enable extra hits for valgrind for debugging purposes |
| (do not use by default) |
| \end_layout |
| |
| \begin_layout Description |
| --enable-sse Enable use of SSE instructions (x86/float only) |
| \end_layout |
| |
| \begin_layout Description |
| --enable-fixed-point |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| fixed-point |
| \end_layout |
| |
| \end_inset |
| |
| Compile Speex for a processor that does not have a floating point unit |
| (FPU) |
| \end_layout |
| |
| \begin_layout Description |
| --enable-arm4-asm Enable assembly specific to the ARMv4 architecture (gcc |
| only) |
| \end_layout |
| |
| \begin_layout Description |
| --enable-arm5e-asm Enable assembly specific to the ARMv5E architecture (gcc |
| only) |
| \end_layout |
| |
| \begin_layout Description |
| --enable-fixed-point-debug Use only for debugging the fixed-point |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| fixed-point |
| \end_layout |
| |
| \end_inset |
| |
| code (very slow) |
| \end_layout |
| |
| \begin_layout Description |
| --enable-ti-c55x Enable support for the TI C5x family |
| \end_layout |
| |
| \begin_layout Description |
| --enable-blackfin-asm Enable assembly specific to the Blackfin DSP architecture |
| (gcc only) |
| \end_layout |
| |
| \begin_layout Section |
| Platforms |
| \end_layout |
| |
| \begin_layout Standard |
| Speex is known to compile and work on a large number of architectures, both |
| floating-point and fixed-point. |
| In general, any architecture that can natively compute the multiplication |
| of two signed 16-bit numbers (32-bit result) and runs at a sufficient clock |
| rate (architecture-dependent) is capable of running Speex. |
| Architectures on which Speex is |
| \series bold |
| known |
| \series default |
| to work (it probably works on many others) are: |
| \end_layout |
| |
| \begin_layout Itemize |
| x86 & x86-64 |
| \end_layout |
| |
| \begin_layout Itemize |
| Power |
| \end_layout |
| |
| \begin_layout Itemize |
| SPARC |
| \end_layout |
| |
| \begin_layout Itemize |
| ARM |
| \end_layout |
| |
| \begin_layout Itemize |
| Blackfin |
| \end_layout |
| |
| \begin_layout Itemize |
| Coldfire (68k family) |
| \end_layout |
| |
| \begin_layout Itemize |
| TI C54xx & C55xx |
| \end_layout |
| |
| \begin_layout Itemize |
| TI C6xxx |
| \end_layout |
| |
| \begin_layout Itemize |
| TriMedia (experimental) |
| \end_layout |
| |
| \begin_layout Standard |
| Operating systems on top of which Speex is known to work include (it probably |
| works on many others): |
| \end_layout |
| |
| \begin_layout Itemize |
| Linux |
| \end_layout |
| |
| \begin_layout Itemize |
| \begin_inset Formula $\mu$ |
| \end_inset |
| |
| Clinux |
| \end_layout |
| |
| \begin_layout Itemize |
| MacOS X |
| \end_layout |
| |
| \begin_layout Itemize |
| BSD |
| \end_layout |
| |
| \begin_layout Itemize |
| Other UNIX/POSIX variants |
| \end_layout |
| |
| \begin_layout Itemize |
| Symbian |
| \end_layout |
| |
| \begin_layout Standard |
| The source code directory include additional information for compiling on |
| certain architectures or operating systems in README.xxx files. |
| \end_layout |
| |
| \begin_layout Section |
| Porting and Optimising |
| \end_layout |
| |
| \begin_layout Standard |
| Here are a few things to consider when porting or optimising Speex for a |
| new platform or an existing one. |
| \end_layout |
| |
| \begin_layout Subsection |
| CPU optimisation |
| \end_layout |
| |
| \begin_layout Standard |
| The single factor that will affect the CPU usage of Speex the most is whether |
| it is compiled for floating point or fixed-point. |
| If your CPU/DSP does not have a floating-point unit FPU, then compiling |
| as fixed-point will be orders of magnitudes faster. |
| If there is an FPU present, then it is important to test which version |
| is faster. |
| On the x86 architecture, floating-point is |
| \series bold |
| generally |
| \series default |
| faster, but not always. |
| To compile Speex as fixed-point, you need to pass --fixed-point to the |
| configure script or define the FIXED_POINT macro for the compiler. |
| As of 1.2beta3, it is now possible to disable the floating-point compatibility |
| API, which means that your code can link without a float emulation library. |
| To do that configure with --disable-float-api or define the DISABLE_FLOAT_API |
| macro. |
| Until the VBR feature is ported to fixed-point, you will also need to configure |
| with --disable-vbr or define DISABLE_VBR. |
| \end_layout |
| |
| \begin_layout Standard |
| Other important things to check on some DSP architectures are: |
| \end_layout |
| |
| \begin_layout Itemize |
| Make sure the cache is set to write-back mode |
| \end_layout |
| |
| \begin_layout Itemize |
| If the chip has SRAM instead of cache, make sure as much code and data are |
| in SRAM, rather than in RAM |
| \end_layout |
| |
| \begin_layout Standard |
| If you are going to be writing assembly, then the following functions are |
| |
| \series bold |
| usually |
| \series default |
| the first ones you should consider optimising: |
| \end_layout |
| |
| \begin_layout Itemize |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| filter_mem16() |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Itemize |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| iir_mem16() |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Itemize |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| vq_nbest() |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Itemize |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| pitch_xcorr() |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Itemize |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| interp_pitch() |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The filtering functions |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| filter_mem16() |
| \end_layout |
| |
| \end_inset |
| |
| and |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| iir_mem16() |
| \end_layout |
| |
| \end_inset |
| |
| are implemented in the direct form II transposed (DF2T). |
| However, for architectures based on multiply-accumulate (MAC), DF2T requires |
| frequent reload of the accumulator, which can make the code very slow. |
| For these architectures (e.g. |
| Blackfin and Coldfire), a better approach is to implement those functions |
| as direct form I (DF1), which is easier to express in terms of MAC. |
| When doing that however, |
| \series bold |
| it is important to make sure that the DF1 implementation still behaves like |
| the original DF2T behaviour when it comes to memory values |
| \series default |
| . |
| This is necessary because the filter is time-varying and must compute exactly |
| the same value (not counting machine rounding) on any encoder or decoder. |
| \end_layout |
| |
| \begin_layout Subsection |
| Memory optimisation |
| \end_layout |
| |
| \begin_layout Standard |
| Memory optimisation is mainly something that should be considered for small |
| embedded platforms. |
| For PCs, Speex is already so tiny that it's just not worth doing any of |
| the things suggested here. |
| There are several ways to reduce the memory usage of Speex, both in terms |
| of code size and data size. |
| For optimising code size, the trick is to first remove features you do |
| not need. |
| Some examples of things that can easily be disabled |
| \series bold |
| if you don't need them |
| \series default |
| are: |
| \end_layout |
| |
| \begin_layout Itemize |
| Wideband support (--disable-wideband) |
| \end_layout |
| |
| \begin_layout Itemize |
| Support for stereo (removing stereo.c) |
| \end_layout |
| |
| \begin_layout Itemize |
| VBR support (--disable-vbr or DISABLE_VBR) |
| \end_layout |
| |
| \begin_layout Itemize |
| Static codebooks that are not needed for the bit-rates you are using (*_table.c |
| files) |
| \end_layout |
| |
| \begin_layout Standard |
| Speex also has several methods for allocating temporary arrays. |
| When using a compiler that supports C99 properly (as of 2007, Microsoft |
| compilers don't, but gcc does), it is best to define VAR_ARRAYS. |
| That makes use of the variable-size array feature of C99. |
| The next best is to define USE_ALLOCA so that Speex can use alloca() to |
| allocate the temporary arrays. |
| Note that on many systems, alloca() is buggy so it may not work. |
| If none of VAR_ARRAYS and USE_ALLOCA are defined, then Speex falls back |
| to allocating a large |
| \begin_inset Quotes eld |
| \end_inset |
| |
| scratch space |
| \begin_inset Quotes erd |
| \end_inset |
| |
| and doing its own internal allocation. |
| The main disadvantage of this solution is that it is wasteful. |
| It needs to allocate enough stack for the worst case scenario (worst bit-rate, |
| highest complexity setting, ...) and by default, the memory isn't shared between |
| multiple encoder/decoder states. |
| Still, if the |
| \begin_inset Quotes eld |
| \end_inset |
| |
| manual |
| \begin_inset Quotes erd |
| \end_inset |
| |
| allocation is the only option left, there are a few things that can be |
| improved. |
| By overriding the speex_alloc_scratch() call in os_support.h, it is possible |
| to always return the same memory area for all states |
| \begin_inset Foot |
| status collapsed |
| |
| \begin_layout Plain Layout |
| In this case, one must be careful with threads |
| \end_layout |
| |
| \end_inset |
| |
| . |
| In addition to that, by redefining the NB_ENC_STACK and NB_DEC_STACK (or |
| similar for wideband), it is possible to only allocate memory for a scenario |
| that is known in advance. |
| In this case, it is important to measure the amount of memory required |
| for the specific sampling rate, bit-rate and complexity level being used. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Command-line encoder/decoder |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Command-line-encoder/decoder" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The base Speex distribution includes a command-line encoder ( |
| \emph on |
| speexenc |
| \emph default |
| ) and decoder ( |
| \emph on |
| speexdec |
| \emph default |
| ). |
| Those tools produce and read Speex files encapsulated in the Ogg container. |
| Although it is possible to encapsulate Speex in any container, Ogg is the |
| recommended container for files. |
| This section describes how to use the command line tools for Speex files |
| in Ogg. |
| \end_layout |
| |
| \begin_layout Section |
| |
| \emph on |
| speexenc |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| speexenc |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The |
| \emph on |
| speexenc |
| \emph default |
| utility is used to create Speex files from raw PCM or wave files. |
| It can be used by calling: |
| \end_layout |
| |
| \begin_layout LyX-Code |
| speexenc [options] input_file output_file |
| \end_layout |
| |
| \begin_layout Standard |
| The value '-' for input_file or output_file corresponds respectively to |
| stdin and stdout. |
| The valid options are: |
| \end_layout |
| |
| \begin_layout Description |
| --narrowband |
| \begin_inset space ~ |
| \end_inset |
| |
| (-n) Tell Speex to treat the input as narrowband (8 kHz). |
| This is the default |
| \end_layout |
| |
| \begin_layout Description |
| --wideband |
| \begin_inset space ~ |
| \end_inset |
| |
| (-w) Tell Speex to treat the input as wideband (16 kHz) |
| \end_layout |
| |
| \begin_layout Description |
| --ultra-wideband |
| \begin_inset space ~ |
| \end_inset |
| |
| (-u) Tell Speex to treat the input as |
| \begin_inset Quotes eld |
| \end_inset |
| |
| ultra-wideband |
| \begin_inset Quotes erd |
| \end_inset |
| |
| (32 kHz) |
| \end_layout |
| |
| \begin_layout Description |
| --quality |
| \begin_inset space ~ |
| \end_inset |
| |
| n Set the encoding quality (0-10), default is 8 |
| \end_layout |
| |
| \begin_layout Description |
| --bitrate |
| \begin_inset space ~ |
| \end_inset |
| |
| n Encoding bit-rate (use bit-rate n or lower) |
| \end_layout |
| |
| \begin_layout Description |
| --vbr Enable VBR (Variable Bit-Rate), disabled by default |
| \end_layout |
| |
| \begin_layout Description |
| --abr |
| \begin_inset space ~ |
| \end_inset |
| |
| n Enable ABR (Average Bit-Rate) at n kbps, disabled by default |
| \end_layout |
| |
| \begin_layout Description |
| --vad Enable VAD (Voice Activity Detection), disabled by default |
| \end_layout |
| |
| \begin_layout Description |
| --dtx Enable DTX (Discontinuous Transmission), disabled by default |
| \end_layout |
| |
| \begin_layout Description |
| --nframes |
| \begin_inset space ~ |
| \end_inset |
| |
| n Pack n frames in each Ogg packet (this saves space at low bit-rates) |
| \end_layout |
| |
| \begin_layout Description |
| --comp |
| \begin_inset space ~ |
| \end_inset |
| |
| n Set encoding speed/quality tradeoff. |
| The higher the value of n, the slower the encoding (default is 3) |
| \end_layout |
| |
| \begin_layout Description |
| -V Verbose operation, print bit-rate currently in use |
| \end_layout |
| |
| \begin_layout Description |
| --help |
| \begin_inset space ~ |
| \end_inset |
| |
| (-h) Print the help |
| \end_layout |
| |
| \begin_layout Description |
| --version |
| \begin_inset space ~ |
| \end_inset |
| |
| (-v) Print version information |
| \end_layout |
| |
| \begin_layout Subsection* |
| Speex comments |
| \end_layout |
| |
| \begin_layout Description |
| --comment Add the given string as an extra comment. |
| This may be used multiple times. |
| |
| \end_layout |
| |
| \begin_layout Description |
| --author Author of this track. |
| |
| \end_layout |
| |
| \begin_layout Description |
| --title Title for this track. |
| |
| \end_layout |
| |
| \begin_layout Subsection* |
| Raw input options |
| \end_layout |
| |
| \begin_layout Description |
| --rate |
| \begin_inset space ~ |
| \end_inset |
| |
| n Sampling rate for raw input |
| \end_layout |
| |
| \begin_layout Description |
| --stereo Consider raw input as stereo |
| \end_layout |
| |
| \begin_layout Description |
| --le Raw input is little-endian |
| \end_layout |
| |
| \begin_layout Description |
| --be Raw input is big-endian |
| \end_layout |
| |
| \begin_layout Description |
| --8bit Raw input is 8-bit unsigned |
| \end_layout |
| |
| \begin_layout Description |
| --16bit Raw input is 16-bit signed |
| \end_layout |
| |
| \begin_layout Section |
| |
| \emph on |
| speexdec |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| speexdec |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The |
| \emph on |
| speexdec |
| \emph default |
| utility is used to decode Speex files and can be used by calling: |
| \end_layout |
| |
| \begin_layout LyX-Code |
| speexdec [options] speex_file [output_file] |
| \end_layout |
| |
| \begin_layout Standard |
| The value '-' for input_file or output_file corresponds respectively to |
| stdin and stdout. |
| Also, when no output_file is specified, the file is played to the soundcard. |
| The valid options are: |
| \end_layout |
| |
| \begin_layout Description |
| --enh enable post-filter (default) |
| \end_layout |
| |
| \begin_layout Description |
| --no-enh disable post-filter |
| \end_layout |
| |
| \begin_layout Description |
| --force-nb Force decoding in narrowband |
| \end_layout |
| |
| \begin_layout Description |
| --force-wb Force decoding in wideband |
| \end_layout |
| |
| \begin_layout Description |
| --force-uwb Force decoding in ultra-wideband |
| \end_layout |
| |
| \begin_layout Description |
| --mono Force decoding in mono |
| \end_layout |
| |
| \begin_layout Description |
| --stereo Force decoding in stereo |
| \end_layout |
| |
| \begin_layout Description |
| --rate |
| \begin_inset space ~ |
| \end_inset |
| |
| n Force decoding at n Hz sampling rate |
| \end_layout |
| |
| \begin_layout Description |
| --packet-loss |
| \begin_inset space ~ |
| \end_inset |
| |
| n Simulate n % random packet loss |
| \end_layout |
| |
| \begin_layout Description |
| -V Verbose operation, print bit-rate currently in use |
| \end_layout |
| |
| \begin_layout Description |
| --help |
| \begin_inset space ~ |
| \end_inset |
| |
| (-h) Print the help |
| \end_layout |
| |
| \begin_layout Description |
| --version |
| \begin_inset space ~ |
| \end_inset |
| |
| (-v) Print version information |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Using the Speex Codec API ( |
| \emph on |
| libspeex |
| \emph default |
| |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| libspeex |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Programming-with-Speex" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The |
| \emph on |
| libspeex |
| \emph default |
| library contains all the functions for encoding and decoding speech with |
| the Speex codec. |
| When linking on a UNIX system, one must add |
| \emph on |
| -lspeex -lm |
| \emph default |
| to the compiler command line. |
| One important thing to know is that |
| \series bold |
| libspeex calls are reentrant, but not thread-safe |
| \series default |
| . |
| That means that it is fine to use calls from many threads, but |
| \series bold |
| calls using the same state from multiple threads must be protected by mutexes |
| \series default |
| . |
| Examples of code can also be found in Appendix |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Sample-code" |
| |
| \end_inset |
| |
| and the complete API documentation is included in the Documentation section |
| of the Speex website (http://www.speex.org/). |
| \end_layout |
| |
| \begin_layout Section |
| Encoding |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sub:Encoding" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| In order to encode speech using Speex, one first needs to: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| #include <speex/speex.h> |
| \end_layout |
| |
| \end_inset |
| |
| Then in the code, a Speex bit-packing struct must be declared, along with |
| a Speex encoder state: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| SpeexBits bits; |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| void *enc_state; |
| \end_layout |
| |
| \end_inset |
| |
| The two are initialized by: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_bits_init(&bits); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| enc_state = speex_encoder_init(&speex_nb_mode); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| For wideband coding, |
| \emph on |
| speex_nb_mode |
| \emph default |
| will be replaced by |
| \emph on |
| speex_wb_mode |
| \emph default |
| . |
| In most cases, you will need to know the frame size used at the sampling |
| rate you are using. |
| You can get that value in the |
| \emph on |
| frame_size |
| \emph default |
| variable (expressed in |
| \series bold |
| samples |
| \series default |
| , not bytes) with: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_encoder_ctl(enc_state,SPEEX_GET_FRAME_SIZE,&frame_size); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| In practice, |
| \emph on |
| frame_size |
| \emph default |
| will correspond to 20 ms when using 8, 16, or 32 kHz sampling rate. |
| There are many parameters that can be set for the Speex encoder, but the |
| most useful one is the quality parameter that controls the quality vs bit-rate |
| tradeoff. |
| This is set by: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_encoder_ctl(enc_state,SPEEX_SET_QUALITY,&quality); |
| \end_layout |
| |
| \end_inset |
| |
| where |
| \emph on |
| quality |
| \emph default |
| is an integer value ranging from 0 to 10 (inclusively). |
| The mapping between quality and bit-rate is described in Fig. |
| |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:quality_vs_bps" |
| |
| \end_inset |
| |
| for narrowband. |
| \end_layout |
| |
| \begin_layout Standard |
| Once the initialization is done, for every input frame: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_bits_reset(&bits); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| speex_encode_int(enc_state, input_frame, &bits); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| nbBytes = speex_bits_write(&bits, byte_ptr, MAX_NB_BYTES); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| where |
| \emph on |
| input_frame |
| \emph default |
| is a |
| \emph on |
| ( |
| \emph default |
| short |
| \emph on |
| *) |
| \emph default |
| pointing to the beginning of a speech frame, |
| \emph on |
| byte_ptr |
| \emph default |
| is a |
| \emph on |
| (char *) |
| \emph default |
| where the encoded frame will be written, |
| \emph on |
| MAX_NB_BYTES |
| \emph default |
| is the maximum number of bytes that can be written to |
| \emph on |
| byte_ptr |
| \emph default |
| without causing an overflow and |
| \emph on |
| nbBytes |
| \emph default |
| is the number of bytes actually written to |
| \emph on |
| byte_ptr |
| \emph default |
| (the encoded size in bytes). |
| Before calling speex_bits_write, it is possible to find the number of bytes |
| that need to be written by calling |
| \family typewriter |
| speex_bits_nbytes(&bits) |
| \family default |
| , which returns a number of bytes. |
| \end_layout |
| |
| \begin_layout Standard |
| It is still possible to use the |
| \emph on |
| speex_encode() |
| \emph default |
| function, which takes a |
| \emph on |
| (float *) |
| \emph default |
| for the audio. |
| However, this would make an eventual port to an FPU-less platform (like |
| ARM) more complicated. |
| Internally, |
| \emph on |
| speex_encode() |
| \emph default |
| and |
| \emph on |
| speex_encode_int() |
| \emph default |
| are processed in the same way. |
| Whether the encoder uses the fixed-point version is only decided by the |
| compile-time flags, not at the API level. |
| \end_layout |
| |
| \begin_layout Standard |
| After you're done with the encoding, free all resources with: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_bits_destroy(&bits); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| speex_encoder_destroy(enc_state); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| That's about it for the encoder. |
| |
| \end_layout |
| |
| \begin_layout Section |
| Decoding |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sub:Decoding" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| In order to decode speech using Speex, you first need to: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| #include <speex/speex.h> |
| \end_layout |
| |
| \end_inset |
| |
| You also need to declare a Speex bit-packing struct |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| SpeexBits bits; |
| \end_layout |
| |
| \end_inset |
| |
| and a Speex decoder state |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| void *dec_state; |
| \end_layout |
| |
| \end_inset |
| |
| The two are initialized by: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_bits_init(&bits); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| dec_state = speex_decoder_init(&speex_nb_mode); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| For wideband decoding, |
| \emph on |
| speex_nb_mode |
| \emph default |
| will be replaced by |
| \emph on |
| speex_wb_mode |
| \emph default |
| . |
| If you need to obtain the size of the frames that will be used by the decoder, |
| you can get that value in the |
| \emph on |
| frame_size |
| \emph default |
| variable (expressed in |
| \series bold |
| samples |
| \series default |
| , not bytes) with: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_decoder_ctl(dec_state, SPEEX_GET_FRAME_SIZE, &frame_size); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| There is also a parameter that can be set for the decoder: whether or not |
| to use a perceptual enhancer. |
| This can be set by: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_decoder_ctl(dec_state, SPEEX_SET_ENH, &enh); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| where |
| \emph on |
| enh |
| \emph default |
| is an int with value 0 to have the enhancer disabled and 1 to have it enabled. |
| As of 1.2-beta1, the default is now to enable the enhancer. |
| \end_layout |
| |
| \begin_layout Standard |
| Again, once the decoder initialization is done, for every input frame: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_bits_read_from(&bits, input_bytes, nbBytes); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| speex_decode_int(dec_state, &bits, output_frame); |
| \end_layout |
| |
| \end_inset |
| |
| where input_bytes is a |
| \emph on |
| (char *) |
| \emph default |
| containing the bit-stream data received for a frame, |
| \emph on |
| nbBytes |
| \emph default |
| is the size (in bytes) of that bit-stream, and |
| \emph on |
| output_frame |
| \emph default |
| is a |
| \emph on |
| (short *) |
| \emph default |
| and points to the area where the decoded speech frame will be written. |
| A NULL value as the second argument indicates that we don't have the bits |
| for the current frame. |
| When a frame is lost, the Speex decoder will do its best to "guess" the |
| correct signal. |
| \end_layout |
| |
| \begin_layout Standard |
| As for the encoder, the |
| \emph on |
| speex_decode() |
| \emph default |
| function can still be used, with a |
| \emph on |
| (float *) |
| \emph default |
| as the output for the audio. |
| After you're done with the decoding, free all resources with: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_bits_destroy(&bits); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| speex_decoder_destroy(dec_state); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Section |
| Codec Options (speex_*_ctl) |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sub:Codec-Options" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Quote |
| \align center |
| |
| \emph on |
| Entities should not be multiplied beyond necessity -- William of Ockham. |
| \end_layout |
| |
| \begin_layout Quote |
| \align center |
| |
| \emph on |
| Just because there's an option for it doesn't mean you have to turn it on |
| -- me. |
| \end_layout |
| |
| \begin_layout Standard |
| The Speex encoder and decoder support many options and requests that can |
| be accessed through the |
| \emph on |
| speex_encoder_ctl |
| \emph default |
| and |
| \emph on |
| speex_decoder_ctl |
| \emph default |
| functions. |
| These functions are similar to the |
| \emph on |
| ioctl |
| \emph default |
| system call and their prototypes are: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| void speex_encoder_ctl(void *encoder, int request, void *ptr); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| void speex_decoder_ctl(void *encoder, int request, void *ptr); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Despite those functions, the defaults are usually good for many applications |
| and |
| \series bold |
| optional settings should only be used when one understands them and knows |
| that they are needed |
| \series default |
| . |
| A common error is to attempt to set many unnecessary settings. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Here is a list of the values allowed for the requests. |
| Some only apply to the encoder or the decoder. |
| Because the last argument is of type |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| void * |
| \end_layout |
| |
| \end_inset |
| |
| , the |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| _ctl() |
| \end_layout |
| |
| \end_inset |
| |
| functions are |
| \series bold |
| not type safe |
| \series default |
| , and should thus be used with care. |
| The type |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| is the same as the C99 |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| int32_t |
| \end_layout |
| |
| \end_inset |
| |
| type. |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_ENH |
| \begin_inset Formula $\ddagger$ |
| \end_inset |
| |
| Set perceptual enhancer |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| perceptual enhancement |
| \end_layout |
| |
| \end_inset |
| |
| to on (1) or off (0) ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| , default is on) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_ENH |
| \begin_inset Formula $\ddagger$ |
| \end_inset |
| |
| Get perceptual enhancer status ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_FRAME_SIZE Get the number of samples per frame for the current |
| mode ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_QUALITY |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set the encoder speech quality ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| from 0 to 10, default is 8) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_QUALITY |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get the current encoder speech quality ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| from 0 to 10) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_MODE |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set the mode number, as specified in the RTP spec ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_MODE |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get the current mode number, as specified in the RTP spec ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_VBR |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set variable bit-rate (VBR) to on (1) or off (0) ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| , default is off) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_VBR |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get variable bit-rate |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| variable bit-rate |
| \end_layout |
| |
| \end_inset |
| |
| (VBR) status ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_VBR_QUALITY |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set the encoder VBR speech quality (float 0.0 to 10.0, default is 8.0) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_VBR_QUALITY |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get the current encoder VBR speech quality (float 0 to 10) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_COMPLEXITY |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set the CPU resources allowed for the encoder ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| from 1 to 10, default is 2) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_COMPLEXITY |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get the CPU resources allowed for the encoder ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| from 1 to 10, default is 2) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_BITRATE |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set the bit-rate to use the closest value not exceeding the parameter ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in bits per second) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_BITRATE Get the current bit-rate in use ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in bits per second) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_SAMPLING_RATE Set real sampling rate ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in Hz) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_SAMPLING_RATE Get real sampling rate ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in Hz) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_RESET_STATE Reset the encoder/decoder state to its original state, |
| clearing all memories (no argument) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_VAD |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set voice activity detection |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| voice activity detection |
| \end_layout |
| |
| \end_inset |
| |
| (VAD) to on (1) or off (0) ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| , default is off) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_VAD |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get voice activity detection (VAD) status ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_DTX |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set discontinuous transmission |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| discontinuous transmission |
| \end_layout |
| |
| \end_inset |
| |
| (DTX) to on (1) or off (0) ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| , default is off) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_DTX |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get discontinuous transmission (DTX) status ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_ABR |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set average bit-rate |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| average bit-rate |
| \end_layout |
| |
| \end_inset |
| |
| (ABR) to a value n in bits per second ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in bits per second) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_ABR |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get average bit-rate (ABR) setting ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in bits per second) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_PLC_TUNING |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Tell the encoder to optimize encoding for a certain percentage of packet |
| loss ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in percent) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_PLC_TUNING |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get the current tuning of the encoder for PLC ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in percent) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_VBR_MAX_BITRATE |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Set the maximum bit-rate allowed in VBR operation ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in bits per second) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_VBR_MAX_BITRATE |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| Get the current maximum bit-rate allowed in VBR operation ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| in bits per second) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SET_HIGHPASS Set the high-pass filter on (1) or off (0) ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| , default is on) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_GET_HIGHPASS Get the current high-pass filter status ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| \begin_inset Formula $\dagger$ |
| \end_inset |
| |
| applies only to the encoder |
| \end_layout |
| |
| \begin_layout Description |
| \begin_inset Formula $\ddagger$ |
| \end_inset |
| |
| applies only to the decoder |
| \end_layout |
| |
| \begin_layout Section |
| Mode queries |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sub:Mode-queries" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Speex modes have a query system similar to the speex_encoder_ctl and speex_decod |
| er_ctl calls. |
| Since modes are read-only, it is only possible to get information about |
| a particular mode. |
| The function used to do that is: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| void speex_mode_query(SpeexMode *mode, int request, void *ptr); |
| \end_layout |
| |
| \end_inset |
| |
| The admissible values for request are (unless otherwise note, the values |
| are returned through |
| \emph on |
| ptr |
| \emph default |
| ): |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_MODE_FRAME_SIZE Get the frame size (in samples) for the mode |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_SUBMODE_BITRATE Get the bit-rate for a submode number specified through |
| |
| \emph on |
| ptr |
| \emph default |
| (integer in bps). |
| |
| \end_layout |
| |
| \begin_layout Section |
| Packing and in-band signalling |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| in-band signalling |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Sometimes it is desirable to pack more than one frame per packet (or other |
| basic unit of storage). |
| The proper way to do it is to call speex_encode |
| \begin_inset Formula $N$ |
| \end_inset |
| |
| times before writing the stream with speex_bits_write. |
| In cases where the number of frames is not determined by an out-of-band |
| mechanism, it is possible to include a terminator code. |
| That terminator consists of the code 15 (decimal) encoded with 5 bits, |
| as shown in Table |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:quality_vs_bps" |
| |
| \end_inset |
| |
| . |
| Note that as of version 1.0.2, calling speex_bits_write automatically inserts |
| the terminator so as to fill the last byte. |
| This doesn't involves any overhead and makes sure Speex can always detect |
| when there is no more frame in a packet. |
| \end_layout |
| |
| \begin_layout Standard |
| It is also possible to send in-band |
| \begin_inset Quotes eld |
| \end_inset |
| |
| messages |
| \begin_inset Quotes erd |
| \end_inset |
| |
| to the other side. |
| All these messages are encoded as |
| \begin_inset Quotes eld |
| \end_inset |
| |
| pseudo-frames |
| \begin_inset Quotes erd |
| \end_inset |
| |
| of mode 14 which contain a 4-bit message type code, followed by the message. |
| Table |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:In-band-signalling-codes" |
| |
| \end_inset |
| |
| lists the available codes, their meaning and the size of the message that |
| follows. |
| Most of these messages are requests that are sent to the encoder or decoder |
| on the other end, which is free to comply or ignore them. |
| By default, all in-band messages are ignored. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float table |
| placement htbp |
| wide false |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="17" columns="3"> |
| <features> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Code |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Size (bits) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Content |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Asks decoder to set perceptual enhancement off (0) or on(1) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Asks (if 1) the encoder to be less |
| \begin_inset Quotes eld |
| \end_inset |
| |
| aggressive |
| \begin_inset Quotes erd |
| \end_inset |
| |
| due to high packet loss |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 2 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Asks encoder to switch to mode N |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Asks encoder to switch to mode N for low-band |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Asks encoder to switch to mode N for high-band |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Asks encoder to switch to quality N for VBR |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 6 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Request acknowledge (0=no, 1=all, 2=only for in-band data) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Asks encoder to set CBR (0), VAD(1), DTX(3), VBR(5), VBR+DTX(7) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 8 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 8 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Transmit (8-bit) character to the other end |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 9 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 8 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Intensity stereo information |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 10 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 16 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Announce maximum bit-rate acceptable (N in bytes/second) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 11 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 16 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 12 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 32 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Acknowledge receiving packet N |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 13 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 32 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 14 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 64 |
| \end_layout |
| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 15 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 64 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| In-band signalling codes |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "cap:In-band-signalling-codes" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Finally, applications may define custom in-band messages using mode 13. |
| The size of the message in bytes is encoded with 5 bits, so that the decoder |
| can skip it if it doesn't know how to interpret it. |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Speech Processing API ( |
| \emph on |
| libspeexdsp |
| \emph default |
| ) |
| \end_layout |
| |
| \begin_layout Standard |
| As of version 1.2beta3, the non-codec parts of the Speex package are now |
| in a separate library called |
| \emph on |
| libspeexdsp |
| \emph default |
| . |
| This library includes the preprocessor, the acoustic echo canceller, the |
| jitter buffer, and the resampler. |
| In a UNIX environment, it can be linked into a program by adding |
| \emph on |
| -lspeexdsp -lm |
| \emph default |
| to the compiler command line. |
| Just like for libspeex, |
| \series bold |
| libspeexdsp calls are reentrant, but not thread-safe |
| \series default |
| . |
| That means that it is fine to use calls from many threads, but |
| \series bold |
| calls using the same state from multiple threads must be protected by mutexes |
| \series default |
| . |
| \end_layout |
| |
| \begin_layout Section |
| Preprocessor |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sub:Preprocessor" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \noindent |
| In order to use the Speex preprocessor |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| preprocessor |
| \end_layout |
| |
| \end_inset |
| |
| , you first need to: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| #include <speex/speex_preprocess.h> |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \noindent |
| Then, a preprocessor state can be created as: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| SpeexPreprocessState *preprocess_state = speex_preprocess_state_init(frame_size, |
| sampling_rate); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \noindent |
| and it is recommended to use the same value for |
| \family typewriter |
| frame_size |
| \family default |
| as is used by the encoder (20 |
| \emph on |
| ms |
| \emph default |
| ). |
| \end_layout |
| |
| \begin_layout Standard |
| For each input frame, you need to call: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_preprocess_run(preprocess_state, audio_frame); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \noindent |
| where |
| \family typewriter |
| audio_frame |
| \family default |
| is used both as input and output. |
| In cases where the output audio is not useful for a certain frame, it is |
| possible to use instead: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_preprocess_estimate_update(preprocess_state, audio_frame); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \noindent |
| This call will update all the preprocessor internal state variables without |
| computing the output audio, thus saving some CPU cycles. |
| \end_layout |
| |
| \begin_layout Standard |
| The behaviour of the preprocessor can be changed using: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_preprocess_ctl(preprocess_state, request, ptr); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \noindent |
| which is used in the same way as the encoder and decoder equivalent. |
| Options are listed in Section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sub:Preprocessor-options" |
| |
| \end_inset |
| |
| . |
| \end_layout |
| |
| \begin_layout Standard |
| The preprocessor state can be destroyed using: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_preprocess_state_destroy(preprocess_state); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Subsection |
| Preprocessor options |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sub:Preprocessor-options" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| As with the codec, the preprocessor also has options that can be controlled |
| using an ioctl()-like call. |
| The available options are: |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_DENOISE Turns denoising on(1) or off(2) ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_DENOISE Get denoising status ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_AGC Turns automatic gain control (AGC) on(1) or off(2) |
| ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_AGC Get AGC status ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_VAD Turns voice activity detector (VAD) on(1) or off(2) |
| ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_VAD Get VAD status ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_AGC_LEVEL |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_AGC_LEVEL |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_DEREVERB Turns reverberation removal on(1) or off(2) |
| ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_DEREVERB Get reverberation removal status ( |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_DEREVERB_LEVEL Not working yet, do not use |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_DEREVERB_LEVEL Not working yet, do not use |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_DEREVERB_DECAY Not working yet, do not use |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_DEREVERB_DECAY Not working yet, do not use |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_PROB_START |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_PROB_START |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_PROB_CONTINUE |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_PROB_CONTINUE |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_NOISE_SUPPRESS Set maximum attenuation of the noise |
| in dB (negative |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_NOISE_SUPPRESS Get maximum attenuation of the noise |
| in dB (negative |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_ECHO_SUPPRESS Set maximum attenuation of the residual |
| echo in dB (negative |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_ECHO_SUPPRESS Get maximum attenuation of the residual |
| echo in dB (negative |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_ECHO_SUPPRESS_ACTIVE Set maximum attenuation of the |
| echo in dB when near end is active (negative |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_ECHO_SUPPRESS_ACTIVE Get maximum attenuation of the |
| echo in dB when near end is active (negative |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| spx_int32_t |
| \end_layout |
| |
| \end_inset |
| |
| ) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_SET_ECHO_STATE Set the associated echo canceller for residual |
| echo suppression (pointer or NULL for no residual echo suppression) |
| \end_layout |
| |
| \begin_layout Description |
| SPEEX_PREPROCESS_GET_ECHO_STATE Get the associated echo canceller (pointer) |
| \end_layout |
| |
| \begin_layout Section |
| Echo Cancellation |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sub:Echo-Cancellation" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The Speex library now includes an echo cancellation |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| echo cancellation |
| \end_layout |
| |
| \end_inset |
| |
| algorithm suitable for Acoustic Echo Cancellation |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| acoustic echo cancellation |
| \end_layout |
| |
| \end_inset |
| |
| (AEC). |
| In order to use the echo canceller, you first need to |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| #include <speex/speex_echo.h> |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Then, an echo canceller state can be created by: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| SpeexEchoState *echo_state = speex_echo_state_init(frame_size, filter_length); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| where |
| \family typewriter |
| frame_size |
| \family default |
| is the amount of data (in samples) you want to process at once and |
| \family typewriter |
| filter_length |
| \family default |
| is the length (in samples) of the echo cancelling filter you want to use |
| (also known as |
| \shape italic |
| tail length |
| \shape default |
| |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| tail length |
| \end_layout |
| |
| \end_inset |
| |
| ). |
| It is recommended to use a frame size in the order of 20 ms (or equal to |
| the codec frame size) and make sure it is easy to perform an FFT of that |
| size (powers of two are better than prime sizes). |
| The recommended tail length is approximately the third of the room reverberatio |
| n time. |
| For example, in a small room, reverberation time is in the order of 300 |
| ms, so a tail length of 100 ms is a good choice (800 samples at 8000 Hz |
| sampling rate). |
| \end_layout |
| |
| \begin_layout Standard |
| Once the echo canceller state is created, audio can be processed by: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_echo_cancellation(echo_state, input_frame, echo_frame, output_frame); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| where |
| \family typewriter |
| input_frame |
| \family default |
| is the audio as captured by the microphone, |
| \family typewriter |
| echo_frame |
| \family default |
| is the signal that was played in the speaker (and needs to be removed) |
| and |
| \family typewriter |
| output_frame |
| \family default |
| is the signal with echo removed. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| One important thing to keep in mind is the relationship between |
| \family typewriter |
| input_frame |
| \family default |
| and |
| \family typewriter |
| echo_frame |
| \family default |
| . |
| It is important that, at any time, any echo that is present in the input |
| has already been sent to the echo canceller as |
| \family typewriter |
| echo_frame |
| \family default |
| . |
| In other words, the echo canceller cannot remove a signal that it hasn't |
| yet received. |
| On the other hand, the delay between the input signal and the echo signal |
| must be small enough because otherwise part of the echo cancellation filter |
| is inefficient. |
| In the ideal case, you code would look like: |
| \begin_inset listings |
| lstparams "breaklines=true" |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| write_to_soundcard(echo_frame, frame_size); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| read_from_soundcard(input_frame, frame_size); |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| speex_echo_cancellation(echo_state, input_frame, echo_frame, output_frame); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| If you wish to further reduce the echo present in the signal, you can do |
| so by associating the echo canceller to the preprocessor (see Section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sub:Preprocessor" |
| |
| \end_inset |
| |
| ). |
| This is done by calling: |
| \begin_inset listings |
| lstparams "breaklines=true" |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_preprocess_ctl(preprocess_state, SPEEX_PREPROCESS_SET_ECHO_STATE,echo_stat |
| e); |
| \end_layout |
| |
| \end_inset |
| |
| in the initialisation. |
| \end_layout |
| |
| \begin_layout Standard |
| As of version 1.2-beta2, there is an alternative, simpler API that can be |
| used instead of |
| \emph on |
| speex_echo_cancellation() |
| \emph default |
| . |
| When audio capture and playback are handled asynchronously (e.g. |
| in different threads or using the |
| \emph on |
| poll() |
| \emph default |
| or |
| \emph on |
| select() |
| \emph default |
| system call), it can be difficult to keep track of what input_frame comes |
| with what echo_frame. |
| Instead, the playback context/thread can simply call: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_echo_playback(echo_state, echo_frame); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| every time an audio frame is played. |
| Then, the capture context/thread calls: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_echo_capture(echo_state, input_frame, output_frame); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| for every frame captured. |
| Internally, |
| \emph on |
| speex_echo_playback() |
| \emph default |
| simply buffers the playback frame so it can be used by |
| \emph on |
| speex_echo_capture() |
| \emph default |
| to call |
| \emph on |
| speex_echo_cancel() |
| \emph default |
| . |
| A side effect of using this alternate API is that the playback audio is |
| delayed by two frames, which is the normal delay caused by the soundcard. |
| When capture and playback are already synchronised, |
| \emph on |
| speex_echo_cancellation() |
| \emph default |
| is preferable since it gives better control on the exact input/echo timing. |
| \end_layout |
| |
| \begin_layout Standard |
| The echo cancellation state can be destroyed with: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_echo_state_destroy(echo_state); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| It is also possible to reset the state of the echo canceller so it can be |
| reused without the need to create another state with: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_echo_state_reset(echo_state); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Subsection |
| Troubleshooting |
| \end_layout |
| |
| \begin_layout Standard |
| There are several things that may prevent the echo canceller from working |
| properly. |
| One of them is a bug (or something suboptimal) in the code, but there are |
| many others you should consider first |
| \end_layout |
| |
| \begin_layout Itemize |
| Using a different soundcard to do the capture and plaback will |
| \series bold |
| not |
| \series default |
| work, regardless of what you may think. |
| The only exception to that is if the two cards can be made to have their |
| sampling clock |
| \begin_inset Quotes eld |
| \end_inset |
| |
| locked |
| \begin_inset Quotes erd |
| \end_inset |
| |
| on the same clock source. |
| If not, the clocks will always have a small amount of drift, which will |
| prevent the echo canceller from adapting. |
| \end_layout |
| |
| \begin_layout Itemize |
| The delay between the record and playback signals must be minimal. |
| Any signal played has to |
| \begin_inset Quotes eld |
| \end_inset |
| |
| appear |
| \begin_inset Quotes erd |
| \end_inset |
| |
| on the playback (far end) signal slightly before the echo canceller |
| \begin_inset Quotes eld |
| \end_inset |
| |
| sees |
| \begin_inset Quotes erd |
| \end_inset |
| |
| it in the near end signal, but excessive delay means that part of the filter |
| length is wasted. |
| In the worst situations, the delay is such that it is longer than the filter |
| length, in which case, no echo can be cancelled. |
| \end_layout |
| |
| \begin_layout Itemize |
| When it comes to echo tail length (filter length), longer is |
| \series bold |
| not |
| \series default |
| better. |
| Actually, the longer the tail length, the longer it takes for the filter |
| to adapt. |
| Of course, a tail length that is too short will not cancel enough echo, |
| but the most common problem seen is that people set a very long tail length |
| and then wonder why no echo is being cancelled. |
| \end_layout |
| |
| \begin_layout Itemize |
| Non-linear distortion cannot (by definition) be modeled by the linear adaptive |
| filter used in the echo canceller and thus cannot be cancelled. |
| Use good audio gear and avoid saturation/clipping. |
| \end_layout |
| |
| \begin_layout Standard |
| Also useful is reading |
| \emph on |
| Echo Cancellation Demystified |
| \emph default |
| by Alexey Frunze |
| \begin_inset Foot |
| status collapsed |
| |
| \begin_layout Plain Layout |
| http://www.embeddedstar.com/articles/2003/7/article20030720-1.html |
| \end_layout |
| |
| \end_inset |
| |
| , which explains the fundamental principles of echo cancellation. |
| The details of the algorithm described in the article are different, but |
| the general ideas of echo cancellation through adaptive filters are the |
| same. |
| \end_layout |
| |
| \begin_layout Standard |
| As of version 1.2beta2, a new |
| \family typewriter |
| echo_diagnostic.m |
| \family default |
| tool is included in the source distribution. |
| The first step is to define DUMP_ECHO_CANCEL_DATA during the build. |
| This causes the echo canceller to automatically save the near-end, far-end |
| and output signals to files (aec_rec.sw aec_play.sw and aec_out.sw). |
| These are exactly what the AEC receives and outputs. |
| From there, it is necessary to start Octave and type: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| lstparams "language=Matlab" |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| echo_diagnostic('aec_rec.sw', 'aec_play.sw', 'aec_diagnostic.sw', 1024); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The value of 1024 is the filter length and can be changed. |
| There will be some (hopefully) useful messages printed and echo cancelled |
| audio will be saved to aec_diagnostic.sw . |
| If even that output is bad (almost no cancellation) then there is probably |
| problem with the playback or recording process. |
| \end_layout |
| |
| \begin_layout Section |
| Jitter Buffer |
| \end_layout |
| |
| \begin_layout Standard |
| The jitter buffer can be enabled by including: |
| \begin_inset listings |
| lstparams "breaklines=true" |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| #include <speex/speex_jitter.h> |
| \end_layout |
| |
| \end_inset |
| |
| and a new jitter buffer state can be initialised by: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| lstparams "breaklines=true" |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| JitterBuffer *state = jitter_buffer_init(step); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| where the |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| step |
| \end_layout |
| |
| \end_inset |
| |
| argument is the default time step (in timestamp units) used for adjusting |
| the delay and doing concealment. |
| A value of 1 is always correct, but higher values may be more convenient |
| sometimes. |
| For example, if you are only able to do concealment on 20ms frames, there |
| is no point in the jitter buffer asking you to do it on one sample. |
| Another example is that for video, it makes no sense to adjust the delay |
| by less than a full frame. |
| The value provided can always be changed at a later time. |
| \end_layout |
| |
| \begin_layout Standard |
| The jitter buffer API is based on the |
| \begin_inset listings |
| inline true |
| status open |
| |
| \begin_layout Plain Layout |
| |
| JitterBufferPacket |
| \end_layout |
| |
| \end_inset |
| |
| type, which is defined as: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| typedef struct { |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| char *data; /* Data bytes contained in the packet */ |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| spx_uint32_t len; /* Length of the packet in bytes */ |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| spx_uint32_t timestamp; /* Timestamp for the packet */ |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| spx_uint32_t span; /* Time covered by the packet (timestamp units) |
| */ |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| } JitterBufferPacket; |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| As an example, for audio the timestamp field would be what is obtained from |
| the RTP timestamp field and the span would be the number of samples that |
| are encoded in the packet. |
| For Speex narrowband, span would be 160 if only one frame is included in |
| the packet. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| When a packet arrives, it need to be inserter into the jitter buffer by: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| JitterBufferPacket packet; |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| /* Fill in each field in the packet struct */ |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| jitter_buffer_put(state, &packet); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| When the decoder is ready to decode a packet the packet to be decoded can |
| be obtained by: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| int start_offset; |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| err = jitter_buffer_get(state, &packet, desired_span, &start_offset); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| If |
| \begin_inset listings |
| inline true |
| status open |
| |
| \begin_layout Plain Layout |
| |
| jitter_buffer_put() |
| \end_layout |
| |
| \end_inset |
| |
| and |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| jitter_buffer_get() |
| \end_layout |
| |
| \end_inset |
| |
| are called from different threads, then |
| \series bold |
| you need to protect the jitter buffer state with a mutex |
| \series default |
| . |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Because the jitter buffer is designed not to use an explicit timer, it needs |
| to be told about the time explicitly. |
| This is done by calling: |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| jitter_buffer_tick(state); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| This needs to be done periodically in the playing thread. |
| This will be the last jitter buffer call before going to sleep (until more |
| data is played back). |
| In some cases, it may be preferable to use |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| jitter_buffer_remaining_span(state, remaining); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The second argument is used to specify that we are still holding data that |
| has not been written to the playback device. |
| For instance, if 256 samples were needed by the soundcard (specified by |
| |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| desired_span |
| \end_layout |
| |
| \end_inset |
| |
| ), but |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| jitter_buffer_get() |
| \end_layout |
| |
| \end_inset |
| |
| returned 320 samples, we would have |
| \begin_inset listings |
| inline true |
| status open |
| |
| \begin_layout Plain Layout |
| |
| remaining=64 |
| \end_layout |
| |
| \end_inset |
| |
| . |
| \end_layout |
| |
| \begin_layout Section |
| Resampler |
| \end_layout |
| |
| \begin_layout Standard |
| Speex includes a resampling modules. |
| To make use of the resampler, it is necessary to include its header file: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| #include <speex/speex_resampler.h> |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| For each stream that is to be resampled, it is necessary to create a resampler |
| state with: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| SpeexResamplerState *resampler; |
| \end_layout |
| |
| \begin_layout Plain Layout |
| |
| resampler = speex_resampler_init(nb_channels, input_rate, output_rate, quality, |
| &err); |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| where |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| nb_channels |
| \end_layout |
| |
| \end_inset |
| |
| is the number of channels that will be used (either interleaved or non-interlea |
| ved), |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| input_rate |
| \end_layout |
| |
| \end_inset |
| |
| is the sampling rate of the input stream, |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| output_rate |
| \end_layout |
| |
| \end_inset |
| |
| is the sampling rate of the output stream and |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| quality |
| \end_layout |
| |
| \end_inset |
| |
| is the requested quality setting (0 to 10). |
| The quality parameter is useful for controlling the quality/complexity/latency |
| tradeoff. |
| Using a higher quality setting means less noise/aliasing, a higher complexity |
| and a higher latency. |
| Usually, a quality of 3 is acceptable for most desktop uses and quality |
| 10 is mostly recommended for pro audio work. |
| Quality 0 usually has a decent sound (certainly better than using linear |
| interpolation resampling), but artifacts may be heard. |
| \end_layout |
| |
| \begin_layout Standard |
| The actual resampling is performed using |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset listings |
| inline false |
| status open |
| |
| \begin_layout Plain Layout |
| |
| err = speex_resampler_process_int(resampler, channelID, in, &in_length, |
| out, &out_length); |
| \end_layout |
| |
| \end_inset |
| |
| where |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| channelID |
| \end_layout |
| |
| \end_inset |
| |
| is the ID of the channel to be processed. |
| For a mono stream, use 0. |
| The |
| \emph on |
| in |
| \emph default |
| pointer points to the first sample of the input buffer for the selected |
| channel and |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| out |
| \end_layout |
| |
| \end_inset |
| |
| points to the first sample of the output. |
| The size of the input and output buffers are specified by |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| in_length |
| \end_layout |
| |
| \end_inset |
| |
| and |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| out_length |
| \end_layout |
| |
| \end_inset |
| |
| respectively. |
| Upon completion, these values are replaced by the number of samples read |
| and written by the resampler. |
| Unless an error occurs, either all input samples will be read or all output |
| samples will be written to (or both). |
| For floating-point samples, the function |
| \begin_inset listings |
| inline true |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_resampler_process_float() |
| \end_layout |
| |
| \end_inset |
| |
| behaves similarly. |
| \end_layout |
| |
| \begin_layout Standard |
| It is also possible to process multiple channels at once. |
| To do that, you can use speex_resampler_process_interleaved_int() or |
| \begin_inset listings |
| inline true |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_resampler_process_interleaved_float() |
| \end_layout |
| |
| \end_inset |
| |
| . |
| The arguments are the same except that there is no |
| \begin_inset listings |
| inline true |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| channelID |
| \end_layout |
| |
| \end_inset |
| |
| argument. |
| Note that the |
| \series bold |
| length parameters are per-channel |
| \series default |
| . |
| So if you have 1024 samples for each of 4 channels, you pass 1024 and not |
| 4096. |
| \end_layout |
| |
| \begin_layout Standard |
| The resampler allows changing the quality and input/output sampling frequencies |
| on the fly without glitches. |
| This can be done with calls such as |
| \begin_inset listings |
| inline true |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_resampler_set_quality() |
| \end_layout |
| |
| \end_inset |
| |
| and |
| \begin_inset listings |
| inline true |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_resampler_set_rate() |
| \end_layout |
| |
| \end_inset |
| |
| . |
| The only side effect is that a new filter will have to be recomputed, consuming |
| many CPU cycles. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| When resampling a file, it is often desirable to have the output file perfectly |
| synchronised with the input. |
| To do that, you need to call |
| \begin_inset listings |
| inline true |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_resampler_skip_zeros() |
| \end_layout |
| |
| \end_inset |
| |
| |
| \series bold |
| before |
| \series default |
| you start processing any samples. |
| For real-time applications (e.g. |
| VoIP), it is not recommended to do that as the first process frame will |
| be shorter to compensate for the delay (the skipped zeros). |
| To destroy a resampler state, just call |
| \begin_inset listings |
| inline true |
| status open |
| |
| \begin_layout Plain Layout |
| |
| speex_resampler_destroy() |
| \end_layout |
| |
| \end_inset |
| |
| . |
| \end_layout |
| |
| \begin_layout Section |
| Ring Buffer |
| \end_layout |
| |
| \begin_layout Standard |
| In some cases, it is necessary to interface components that use different |
| block sizes. |
| For example, it is possible that the soundcard does not support reading/writing |
| in blocks of 20 |
| \begin_inset space ~ |
| \end_inset |
| |
| ms or sometimes, complicated resampling ratios mean that the blocks don't |
| always have the same time. |
| In thoses cases, it is often necessary to buffer a bit of audio using a |
| ring buffer. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Formats and standards |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| standards |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Formats-and-standards" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Speex can encode speech in both narrowband and wideband and provides different |
| bit-rates. |
| However, not all features need to be supported by a certain implementation |
| or device. |
| In order to be called |
| \begin_inset Quotes eld |
| \end_inset |
| |
| Speex compatible |
| \begin_inset Quotes erd |
| \end_inset |
| |
| (whatever that means), an implementation must implement at least a basic |
| set of features. |
| \end_layout |
| |
| \begin_layout Standard |
| At the minimum, all narrowband modes of operation MUST be supported at the |
| decoder. |
| This includes the decoding of a wideband bit-stream by the narrowband decoder |
| \begin_inset Foot |
| status collapsed |
| |
| \begin_layout Plain Layout |
| The wideband bit-stream contains an embedded narrowband bit-stream which |
| can be decoded alone |
| \end_layout |
| |
| \end_inset |
| |
| . |
| If present, a wideband decoder MUST be able to decode a narrowband stream, |
| and MAY either be able to decode all wideband modes or be able to decode |
| the embedded narrowband part of all modes (which includes ignoring the |
| high-band bits). |
| \end_layout |
| |
| \begin_layout Standard |
| For encoders, at least one narrowband or wideband mode MUST be supported. |
| The main reason why all encoding modes do not have to be supported is that |
| some platforms may not be able to handle the complexity of encoding in |
| some modes. |
| \end_layout |
| |
| \begin_layout Section |
| RTP |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| RTP |
| \end_layout |
| |
| \end_inset |
| |
| Payload Format |
| \end_layout |
| |
| \begin_layout Standard |
| The RTP payload draft is included in appendix |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:IETF-draft" |
| |
| \end_inset |
| |
| and the latest version is available at |
| \begin_inset Flex URL |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| http://www.speex.org/drafts/latest |
| \end_layout |
| |
| \end_inset |
| |
| . |
| This draft has been sent (2003/02/26) to the Internet Engineering Task |
| Force (IETF) and will be discussed at the March 18th meeting in San Francisco. |
| |
| \end_layout |
| |
| \begin_layout Section |
| MIME Type |
| \end_layout |
| |
| \begin_layout Standard |
| For now, you should use the MIME type audio/x-speex for Speex-in-Ogg. |
| We will apply for type |
| \family typewriter |
| audio/speex |
| \family default |
| in the near future. |
| \end_layout |
| |
| \begin_layout Section |
| Ogg |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| Ogg |
| \end_layout |
| |
| \end_inset |
| |
| file format |
| \end_layout |
| |
| \begin_layout Standard |
| Speex bit-streams can be stored in Ogg files. |
| In this case, the first packet of the Ogg file contains the Speex header |
| described in table |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:ogg_speex_header" |
| |
| \end_inset |
| |
| . |
| All integer fields in the headers are stored as little-endian. |
| The |
| \family typewriter |
| speex_string |
| \family default |
| field must contain the |
| \begin_inset Quotes eld |
| \end_inset |
| |
| |
| \family typewriter |
| Speex |
| \family default |
| |
| \begin_inset space ~ |
| \end_inset |
| |
| |
| \begin_inset space ~ |
| \end_inset |
| |
| |
| \begin_inset space ~ |
| \end_inset |
| |
| |
| \begin_inset Quotes erd |
| \end_inset |
| |
| (with 3 trailing spaces), which identifies the bit-stream. |
| The next field, |
| \family typewriter |
| speex_version |
| \family default |
| contains the version of Speex that encoded the file. |
| For now, refer to speex_header.[ch] for more info. |
| The |
| \emph on |
| beginning of stream |
| \emph default |
| ( |
| \family typewriter |
| b_o_s |
| \family default |
| ) flag is set to 1 for the header. |
| The header packet has |
| \family typewriter |
| packetno=0 |
| \family default |
| and |
| \family typewriter |
| granulepos=0 |
| \family default |
| . |
| \end_layout |
| |
| \begin_layout Standard |
| The second packet contains the Speex comment header. |
| The format used is the Vorbis comment format described here: http://www.xiph.org/ |
| ogg/vorbis/doc/v-comment.html . |
| This packet has |
| \family typewriter |
| packetno=1 |
| \family default |
| and |
| \family typewriter |
| granulepos=0 |
| \family default |
| . |
| \end_layout |
| |
| \begin_layout Standard |
| The third and subsequent packets each contain one or more (number found |
| in header) Speex frames. |
| These are identified with |
| \family typewriter |
| packetno |
| \family default |
| starting from 2 and the |
| \family typewriter |
| granulepos |
| \family default |
| is the number of the last sample encoded in that packet. |
| The last of these packets has the |
| \emph on |
| end of stream |
| \emph default |
| ( |
| \family typewriter |
| e_o_s |
| \family default |
| ) flag is set to 1. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float table |
| placement htbp |
| wide true |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="16" columns="3"> |
| <features> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
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| <row> |
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| |
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| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
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| |
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| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| rate |
| \end_layout |
| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| int |
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| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
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| 4 |
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| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| mode |
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| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
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| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
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| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| mode_bitstream_version |
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| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| int |
| \end_layout |
| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
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| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| nb_channels |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| int |
| \end_layout |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| bitrate |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| int |
| \end_layout |
| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
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| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame_size |
| \end_layout |
| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| int |
| \end_layout |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
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| 4 |
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| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
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| vbr |
| \end_layout |
| |
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| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
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| int |
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| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
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| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frames_per_packet |
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| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| int |
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| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
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| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| extra_headers |
| \end_layout |
| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| int |
| \end_layout |
| |
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| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
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| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| int |
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| |
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| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
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| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved2 |
| \end_layout |
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| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| int |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Ogg/Speex header packet |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "cap:ogg_speex_header" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| clearpage |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Introduction to CELP Coding |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| CELP |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Introduction-to-CELP" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Quote |
| \align center |
| |
| \emph on |
| Do not meddle in the affairs of poles, for they are subtle and quick to |
| leave the unit circle. |
| \end_layout |
| |
| \begin_layout Standard |
| Speex is based on CELP, which stands for Code Excited Linear Prediction. |
| This section attempts to introduce the principles behind CELP, so if you |
| are already familiar with CELP, you can safely skip to section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Speex-narrowband-mode" |
| |
| \end_inset |
| |
| . |
| The CELP technique is based on three ideas: |
| \end_layout |
| |
| \begin_layout Enumerate |
| The use of a linear prediction (LP) model to model the vocal tract |
| \end_layout |
| |
| \begin_layout Enumerate |
| The use of (adaptive and fixed) codebook entries as input (excitation) of |
| the LP model |
| \end_layout |
| |
| \begin_layout Enumerate |
| The search performed in closed-loop in a |
| \begin_inset Quotes eld |
| \end_inset |
| |
| perceptually weighted domain |
| \begin_inset Quotes erd |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| This section describes the basic ideas behind CELP. |
| This is still a work in progress. |
| \end_layout |
| |
| \begin_layout Section |
| Source-Filter Model of Speech Prediction |
| \end_layout |
| |
| \begin_layout Standard |
| The source-filter model of speech production assumes that the vocal cords |
| are the source of spectrally flat sound (the excitation signal), and that |
| the vocal tract acts as a filter to spectrally shape the various sounds |
| of speech. |
| While still an approximation, the model is widely used in speech coding |
| because of its simplicity.Its use is also the reason why most speech codecs |
| (Speex included) perform badly on music signals. |
| The different phonemes can be distinguished by their excitation (source) |
| and spectral shape (filter). |
| Voiced sounds (e.g. |
| vowels) have an excitation signal that is periodic and that can be approximated |
| by an impulse train in the time domain or by regularly-spaced harmonics |
| in the frequency domain. |
| On the other hand, fricatives (such as the "s", "sh" and "f" sounds) have |
| an excitation signal that is similar to white Gaussian noise. |
| So called voice fricatives (such as "z" and "v") have excitation signal |
| composed of an harmonic part and a noisy part. |
| \end_layout |
| |
| \begin_layout Standard |
| The source-filter model is usually tied with the use of Linear prediction. |
| The CELP model is based on source-filter model, as can be seen from the |
| CELP decoder illustrated in Figure |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "fig:The-CELP-model" |
| |
| \end_inset |
| |
| . |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float figure |
| wide false |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Graphics |
| filename celp_decoder.eps |
| width 45page% |
| keepAspectRatio |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| The CELP model of speech synthesis (decoder) |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "fig:The-CELP-model" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Section |
| Linear Prediction Coefficients (LPC) |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| linear prediction |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Linear prediction is at the base of many speech coding techniques, including |
| CELP. |
| The idea behind it is to predict the signal |
| \begin_inset Formula $x[n]$ |
| \end_inset |
| |
| using a linear combination of its past samples: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Formula \[ |
| y[n]=\sum_{i=1}^{N}a_{i}x[n-i]\] |
| |
| \end_inset |
| |
| where |
| \begin_inset Formula $y[n]$ |
| \end_inset |
| |
| is the linear prediction of |
| \begin_inset Formula $x[n]$ |
| \end_inset |
| |
| . |
| The prediction error is thus given by: |
| \begin_inset Formula \[ |
| e[n]=x[n]-y[n]=x[n]-\sum_{i=1}^{N}a_{i}x[n-i]\] |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The goal of the LPC analysis is to find the best prediction coefficients |
| |
| \begin_inset Formula $a_{i}$ |
| \end_inset |
| |
| which minimize the quadratic error function: |
| \begin_inset Formula \[ |
| E=\sum_{n=0}^{L-1}\left[e[n]\right]^{2}=\sum_{n=0}^{L-1}\left[x[n]-\sum_{i=1}^{N}a_{i}x[n-i]\right]^{2}\] |
| |
| \end_inset |
| |
| That can be done by making all derivatives |
| \begin_inset Formula $\frac{\partial E}{\partial a_{i}}$ |
| \end_inset |
| |
| equal to zero: |
| \begin_inset Formula \[ |
| \frac{\partial E}{\partial a_{i}}=\frac{\partial}{\partial a_{i}}\sum_{n=0}^{L-1}\left[x[n]-\sum_{i=1}^{N}a_{i}x[n-i]\right]^{2}=0\] |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| For an order |
| \begin_inset Formula $N$ |
| \end_inset |
| |
| filter, the filter coefficients |
| \begin_inset Formula $a_{i}$ |
| \end_inset |
| |
| are found by solving the system |
| \begin_inset Formula $N\times N$ |
| \end_inset |
| |
| linear system |
| \begin_inset Formula $\mathbf{Ra}=\mathbf{r}$ |
| \end_inset |
| |
| , where |
| \begin_inset Formula \[ |
| \mathbf{R}=\left[\begin{array}{cccc} |
| R(0) & R(1) & \cdots & R(N-1)\\ |
| R(1) & R(0) & \cdots & R(N-2)\\ |
| \vdots & \vdots & \ddots & \vdots\\ |
| R(N-1) & R(N-2) & \cdots & R(0)\end{array}\right]\] |
| |
| \end_inset |
| |
| |
| \begin_inset Formula \[ |
| \mathbf{r}=\left[\begin{array}{c} |
| R(1)\\ |
| R(2)\\ |
| \vdots\\ |
| R(N)\end{array}\right]\] |
| |
| \end_inset |
| |
| with |
| \begin_inset Formula $R(m)$ |
| \end_inset |
| |
| , the auto-correlation |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| auto-correlation |
| \end_layout |
| |
| \end_inset |
| |
| of the signal |
| \begin_inset Formula $x[n]$ |
| \end_inset |
| |
| , computed as: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Formula \[ |
| R(m)=\sum_{i=0}^{N-1}x[i]x[i-m]\] |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Because |
| \begin_inset Formula $\mathbf{R}$ |
| \end_inset |
| |
| is Hermitian Toeplitz, the Levinson-Durbin |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| Levinson-Durbin |
| \end_layout |
| |
| \end_inset |
| |
| algorithm can be used, making the solution to the problem |
| \begin_inset Formula $\mathcal{O}\left(N^{2}\right)$ |
| \end_inset |
| |
| instead of |
| \begin_inset Formula $\mathcal{O}\left(N^{3}\right)$ |
| \end_inset |
| |
| . |
| Also, it can be proven that all the roots of |
| \begin_inset Formula $A(z)$ |
| \end_inset |
| |
| are within the unit circle, which means that |
| \begin_inset Formula $1/A(z)$ |
| \end_inset |
| |
| is always stable. |
| This is in theory; in practice because of finite precision, there are two |
| commonly used techniques to make sure we have a stable filter. |
| First, we multiply |
| \begin_inset Formula $R(0)$ |
| \end_inset |
| |
| by a number slightly above one (such as 1.0001), which is equivalent to |
| adding noise to the signal. |
| Also, we can apply a window to the auto-correlation, which is equivalent |
| to filtering in the frequency domain, reducing sharp resonances. |
| \end_layout |
| |
| \begin_layout Section |
| Pitch Prediction |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| pitch |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| During voiced segments, the speech signal is periodic, so it is possible |
| to take advantage of that property by approximating the excitation signal |
| |
| \begin_inset Formula $e[n]$ |
| \end_inset |
| |
| by a gain times the past of the excitation: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Formula \[ |
| e[n]\simeq p[n]=\beta e[n-T]\ ,\] |
| |
| \end_inset |
| |
| where |
| \begin_inset Formula $T$ |
| \end_inset |
| |
| is the pitch period, |
| \begin_inset Formula $\beta$ |
| \end_inset |
| |
| is the pitch gain. |
| We call that long-term prediction since the excitation is predicted from |
| |
| \begin_inset Formula $e[n-T]$ |
| \end_inset |
| |
| with |
| \begin_inset Formula $T\gg N$ |
| \end_inset |
| |
| . |
| \end_layout |
| |
| \begin_layout Section |
| Innovation Codebook |
| \end_layout |
| |
| \begin_layout Standard |
| The final excitation |
| \begin_inset Formula $e[n]$ |
| \end_inset |
| |
| will be the sum of the pitch prediction and an |
| \emph on |
| innovation |
| \emph default |
| signal |
| \begin_inset Formula $c[n]$ |
| \end_inset |
| |
| taken from a fixed codebook, hence the name |
| \emph on |
| Code |
| \emph default |
| Excited Linear Prediction. |
| The final excitation is given by |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Formula \[ |
| e[n]=p[n]+c[n]=\beta e[n-T]+c[n]\ .\] |
| |
| \end_inset |
| |
| The quantization of |
| \begin_inset Formula $c[n]$ |
| \end_inset |
| |
| is where most of the bits in a CELP codec are allocated. |
| It represents the information that couldn't be obtained either from linear |
| prediction or pitch prediction. |
| In the |
| \emph on |
| z |
| \emph default |
| -domain we can represent the final signal |
| \begin_inset Formula $X(z)$ |
| \end_inset |
| |
| as |
| \begin_inset Formula \[ |
| X(z)=\frac{C(z)}{A(z)\left(1-\beta z^{-T}\right)}\] |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Section |
| Noise Weighting |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| error weighting |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| analysis-by-synthesis |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| Most (if not all) modern audio codecs attempt to |
| \begin_inset Quotes eld |
| \end_inset |
| |
| shape |
| \begin_inset Quotes erd |
| \end_inset |
| |
| the noise so that it appears mostly in the frequency regions where the |
| ear cannot detect it. |
| For example, the ear is more tolerant to noise in parts of the spectrum |
| that are louder and |
| \emph on |
| vice versa |
| \emph default |
| . |
| In order to maximize speech quality, CELP codecs minimize the mean square |
| of the error (noise) in the perceptually weighted domain. |
| This means that a perceptual noise weighting filter |
| \begin_inset Formula $W(z)$ |
| \end_inset |
| |
| is applied to the error signal in the encoder. |
| In most CELP codecs, |
| \begin_inset Formula $W(z)$ |
| \end_inset |
| |
| is a pole-zero weighting filter derived from the linear prediction coefficients |
| (LPC), generally using bandwidth expansion. |
| Let the spectral envelope be represented by the synthesis filter |
| \begin_inset Formula $1/A(z)$ |
| \end_inset |
| |
| , CELP codecs typically derive the noise weighting filter as |
| \begin_inset Formula \begin{equation} |
| W(z)=\frac{A(z/\gamma_{1})}{A(z/\gamma_{2})}\ ,\label{eq:gamma-weighting}\end{equation} |
| |
| \end_inset |
| |
| where |
| \begin_inset Formula $\gamma_{1}=0.9$ |
| \end_inset |
| |
| and |
| \begin_inset Formula $\gamma_{2}=0.6$ |
| \end_inset |
| |
| in the Speex reference implementation. |
| If a filter |
| \begin_inset Formula $A(z)$ |
| \end_inset |
| |
| has (complex) poles at |
| \begin_inset Formula $p_{i}$ |
| \end_inset |
| |
| in the |
| \begin_inset Formula $z$ |
| \end_inset |
| |
| -plane, the filter |
| \begin_inset Formula $A(z/\gamma)$ |
| \end_inset |
| |
| will have its poles at |
| \begin_inset Formula $p'_{i}=\gamma p_{i}$ |
| \end_inset |
| |
| , making it a flatter version of |
| \begin_inset Formula $A(z)$ |
| \end_inset |
| |
| . |
| \end_layout |
| |
| \begin_layout Standard |
| The weighting filter is applied to the error signal used to optimize the |
| codebook search through analysis-by-synthesis (AbS). |
| This results in a spectral shape of the noise that tends towards |
| \begin_inset Formula $1/W(z)$ |
| \end_inset |
| |
| . |
| While the simplicity of the model has been an important reason for the |
| success of CELP, it remains that |
| \begin_inset Formula $W(z)$ |
| \end_inset |
| |
| is a very rough approximation for the perceptually optimal noise weighting |
| function. |
| Fig. |
| |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:Standard-noise-shaping" |
| |
| \end_inset |
| |
| illustrates the noise shaping that results from Eq. |
| |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "eq:gamma-weighting" |
| |
| \end_inset |
| |
| . |
| Throughout this paper, we refer to |
| \begin_inset Formula $W(z)$ |
| \end_inset |
| |
| as the noise weighting filter and to |
| \begin_inset Formula $1/W(z)$ |
| \end_inset |
| |
| as the noise shaping filter (or curve). |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float figure |
| wide false |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Graphics |
| filename ref_shaping.eps |
| width 45page% |
| keepAspectRatio |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Standard noise shaping in CELP. |
| Arbitrary y-axis offset. |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "cap:Standard-noise-shaping" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Section |
| Analysis-by-Synthesis |
| \end_layout |
| |
| \begin_layout Standard |
| One of the main principles behind CELP is called Analysis-by-Synthesis (AbS), |
| meaning that the encoding (analysis) is performed by perceptually optimising |
| the decoded (synthesis) signal in a closed loop. |
| In theory, the best CELP stream would be produced by trying all possible |
| bit combinations and selecting the one that produces the best-sounding |
| decoded signal. |
| This is obviously not possible in practice for two reasons: the required |
| complexity is beyond any currently available hardware and the |
| \begin_inset Quotes eld |
| \end_inset |
| |
| best sounding |
| \begin_inset Quotes erd |
| \end_inset |
| |
| selection criterion implies a human listener. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| In order to achieve real-time encoding using limited computing resources, |
| the CELP optimisation is broken down into smaller, more manageable, sequential |
| searches using the perceptual weighting function described earlier. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| The Speex Decoder Specification |
| \end_layout |
| |
| \begin_layout Section |
| Narrowband decoder |
| \end_layout |
| |
| \begin_layout Standard |
| <Insert decoder figure here> |
| \end_layout |
| |
| \begin_layout Subsection |
| Narrowband modes |
| \end_layout |
| |
| \begin_layout Standard |
| There are 7 different narrowband bit-rates defined for Speex, ranging from |
| 250 bps to 24.6 kbps, although the modes below 5.9 kbps should not be used |
| for speech. |
| The bit-allocation for each mode is detailed in table |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:bits-narrowband" |
| |
| \end_inset |
| |
| . |
| Each frame starts with the mode ID encoded with 4 bits which allows a range |
| from 0 to 15, though only the first 7 values are used (the others are reserved). |
| The parameters are listed in the table in the order they are packed in |
| the bit-stream. |
| All frame-based parameters are packed before sub-frame parameters. |
| The parameters for a certain sub-frame are all packed before the following |
| sub-frame is packed. |
| The |
| \begin_inset Quotes eld |
| \end_inset |
| |
| OL |
| \begin_inset Quotes erd |
| \end_inset |
| |
| in the parameter description means that the parameter is an open loop estimatio |
| n based on the whole frame. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float table |
| placement h |
| wide true |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="12" columns="11"> |
| <features> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Parameter |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Update rate |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 2 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 6 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 8 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Wideband bit |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Mode ID |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| LSP |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 18 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 18 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 18 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 18 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 30 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 30 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 30 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 18 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| OL pitch |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| OL pitch gain |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| OL Exc gain |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Fine pitch |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| sub-frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Pitch gain |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| sub-frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Innovation gain |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| sub-frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Innovation VQ |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| sub-frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 16 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 20 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 35 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 48 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 64 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 96 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 10 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Total |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 43 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 119 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 160 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 220 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 300 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 364 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 492 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 79 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Bit allocation for narrowband modes |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "cap:bits-narrowband" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Subsection |
| LSP decoding |
| \end_layout |
| |
| \begin_layout Standard |
| Depending on the mode, LSP parameters are encoded using either 18 bits or |
| 30 bits. |
| \end_layout |
| |
| \begin_layout Standard |
| Interpolation |
| \end_layout |
| |
| \begin_layout Standard |
| Safe margin |
| \end_layout |
| |
| \begin_layout Subsection |
| Adaptive codebook |
| \end_layout |
| |
| \begin_layout Standard |
| For rates of 8 kbit/s and above, the pitch period is encoded for each subframe. |
| The real period is |
| \begin_inset Formula $T=p_{i}+17$ |
| \end_inset |
| |
| where |
| \begin_inset Formula $p_{i}$ |
| \end_inset |
| |
| is a value encoded with 7 bits and 17 corresponds to the minimum pitch. |
| The maximum period is 144. |
| At 5.95 kbit/s (mode 2), the pitch period is similarly encoded, but only |
| once for the frame. |
| Each sub-frame then has a 2-bit offset that is added to the pitch value |
| of the frame. |
| In that case, the pitch for each sub-frame is equal to |
| \begin_inset Formula $T-1+offset$ |
| \end_inset |
| |
| . |
| For rates below 5.95 kbit/s, only the per-frame pitch is used and the pitch |
| is constant for all sub-frames. |
| \end_layout |
| |
| \begin_layout Standard |
| Speex uses a 3-tap predictor for rates of 5.95 kbit/s and above. |
| The three gain values are obtained from a 5-bit or a 7-bit codebook, depending |
| on the mode. |
| |
| \end_layout |
| |
| \begin_layout Subsection |
| Innovation codebook |
| \end_layout |
| |
| \begin_layout Standard |
| Split codebook, size and entries depend on bit-rate |
| \end_layout |
| |
| \begin_layout Standard |
| a 5-bit gain is encoder on a per-frame basis |
| \end_layout |
| |
| \begin_layout Standard |
| Depending on the mode, higher resolution per sub-frame |
| \end_layout |
| |
| \begin_layout Standard |
| innovation sub-vectors concatenated, gain applied |
| \end_layout |
| |
| \begin_layout Subsection |
| Perceptual enhancement |
| \end_layout |
| |
| \begin_layout Standard |
| Optional, implementation-defined. |
| |
| \end_layout |
| |
| \begin_layout Subsection |
| Bit-stream definition |
| \end_layout |
| |
| \begin_layout Standard |
| This section defines the bit-stream that is transmitted on the wire. |
| One speex packet consist of 1 frame header and 4 sub-frames: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="1" columns="5"> |
| <features> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Frame Header |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Subframe 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Subframe2 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Subframe 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Subframe 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The frame header is variable length, depending on decoding mode and submode. |
| The narrowband frame header is defined as follows: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="1" columns="6"> |
| <features> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| wb bit |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| modeid |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| LSP |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| OL-pitch |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| OL-pitchgain |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| OL ExcGain |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| wb-bit: Wideband bit (1 bit) 0=narrowband, 1=wideband |
| \end_layout |
| |
| \begin_layout Standard |
| modeid: Mode identifier (4 bits) |
| \end_layout |
| |
| \begin_layout Standard |
| LSP: Line Spectral Pairs (0, 18 or 30 bits) |
| \end_layout |
| |
| \begin_layout Standard |
| OL-pitch: Open Loop Pitch (0 or 7 bits) |
| \end_layout |
| |
| \begin_layout Standard |
| OL-pitchgain: Open Loop Pitch Gain (0 or 4 bits) |
| \end_layout |
| |
| \begin_layout Standard |
| OL-ExcGain: Open Loop Excitation Gain (0 or 5 bits) |
| \end_layout |
| |
| \begin_layout Standard |
| ... |
| \end_layout |
| |
| \begin_layout Standard |
| Each subframe is defined as follows: |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="1" columns="4"> |
| <features> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <column alignment="center" valignment="top" width="0"> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| FinePitch |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| PitchGain |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| InnovationGain |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Innovation VQ |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| FinePitch: (0 or 7 bits) |
| \end_layout |
| |
| \begin_layout Standard |
| PitchGain: (0, 5, or 7 bits) |
| \end_layout |
| |
| \begin_layout Standard |
| Innovation Gain: (0, 1, 3 bits) |
| \end_layout |
| |
| \begin_layout Standard |
| Innovation VQ: (0-96 bits) |
| \end_layout |
| |
| \begin_layout Standard |
| ... |
| \end_layout |
| |
| \begin_layout Subsection |
| Sample decoder |
| \end_layout |
| |
| \begin_layout Standard |
| This section contains some sample source code, showing how a basic Speex |
| decoder can be implemented. |
| The sample decoder is narrowband submode 3 only, and with no advanced features |
| like enhancement, vbr etc. |
| \end_layout |
| |
| \begin_layout Standard |
| ... |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "nb_celp.c" |
| lstparams "caption={Sample Decoder}" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Subsection |
| Lookup tables |
| \end_layout |
| |
| \begin_layout Standard |
| The Speex decoder includes a set of lookup tables and codebooks, which are |
| used to convert between values of different domains. |
| This includes: |
| \end_layout |
| |
| \begin_layout Standard |
| - Excitation 10x16 (3200 bps) |
| \end_layout |
| |
| \begin_layout Standard |
| - Excitation 10x32 (4000 bps) |
| \end_layout |
| |
| \begin_layout Standard |
| - Excitation 20x32 (2000 bps) |
| \end_layout |
| |
| \begin_layout Standard |
| - Excitation 5x256 (12800 bps) |
| \end_layout |
| |
| \begin_layout Standard |
| - Excitation 5x64 (9600 bps) |
| \end_layout |
| |
| \begin_layout Standard |
| - Excitation 8x128 (7000 bps) |
| \end_layout |
| |
| \begin_layout Standard |
| - Codebook for 3-tap pitch prediction gain (Normal and Low Bitrate) |
| \end_layout |
| |
| \begin_layout Standard |
| - Codebook for LSPs in narrowband CELP mode |
| \end_layout |
| |
| \begin_layout Standard |
| ... |
| \end_layout |
| |
| \begin_layout Standard |
| The exact lookup tables are included here for reference. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../libspeex/exc_5_64_table.c" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../libspeex/exc_5_256_table.c" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../libspeex/exc_8_128_table.c" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../libspeex/exc_10_16_table.c" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../libspeex/exc_10_32_table.c" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../libspeex/exc_20_32_table.c" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../libspeex/gain_table.c" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../libspeex/gain_table_lbr.c" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../libspeex/lsp_tables_nb.c" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Section |
| Wideband embedded decoder |
| \end_layout |
| |
| \begin_layout Standard |
| QMF filter. |
| Narrowband signal decoded using narrowband decoder |
| \end_layout |
| |
| \begin_layout Standard |
| For the high band, the decoder is similar to the narrowband decoder, with |
| the main difference being that there is no adaptive codebook. |
| \end_layout |
| |
| \begin_layout Standard |
| Gain is per-subframe |
| \end_layout |
| |
| \begin_layout Chapter |
| Speex narrowband mode |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Speex-narrowband-mode" |
| |
| \end_inset |
| |
| |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| narrowband |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| This section looks at how Speex works for narrowband ( |
| \begin_inset Formula $8\:\mathrm{kHz}$ |
| \end_inset |
| |
| sampling rate) operation. |
| The frame size for this mode is |
| \begin_inset Formula $20\:\mathrm{ms}$ |
| \end_inset |
| |
| , corresponding to 160 samples. |
| Each frame is also subdivided into 4 sub-frames of 40 samples each. |
| \end_layout |
| |
| \begin_layout Standard |
| Also many design decisions were based on the original goals and assumptions: |
| \end_layout |
| |
| \begin_layout Itemize |
| Minimizing the amount of information extracted from past frames (for robustness |
| to packet loss) |
| \end_layout |
| |
| \begin_layout Itemize |
| Dynamically-selectable codebooks (LSP, pitch and innovation) |
| \end_layout |
| |
| \begin_layout Itemize |
| sub-vector fixed (innovation) codebooks |
| \end_layout |
| |
| \begin_layout Section |
| Whole-Frame Analysis |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| linear prediction |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| In narrowband, Speex frames are 20 ms long (160 samples) and are subdivided |
| in 4 sub-frames of 5 ms each (40 samples). |
| For most narrowband bit-rates (8 kbps and above), the only parameters encoded |
| at the frame level are the Line Spectral Pairs (LSP) and a global excitation |
| gain |
| \begin_inset Formula $g_{frame}$ |
| \end_inset |
| |
| , as shown in Fig. |
| |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:Frame-open-loop-analysis" |
| |
| \end_inset |
| |
| . |
| All other parameters are encoded at the sub-frame level. |
| \end_layout |
| |
| \begin_layout Standard |
| Linear prediction analysis is performed once per frame using an asymmetric |
| Hamming window centered on the fourth sub-frame. |
| Because linear prediction coefficients (LPC) are not robust to quantization, |
| they are first converted to line spectral pairs (LSP) |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| line spectral pair |
| \end_layout |
| |
| \end_inset |
| |
| . |
| The LSP's are considered to be associated to the |
| \begin_inset Formula $4^{th}$ |
| \end_inset |
| |
| sub-frames and the LSP's associated to the first 3 sub-frames are linearly |
| interpolated using the current and previous LSP coefficients. |
| The LSP coefficients and converted back to the LPC filter |
| \begin_inset Formula $\hat{A}(z)$ |
| \end_inset |
| |
| . |
| The non-quantized interpolated filter is denoted |
| \begin_inset Formula $A(z)$ |
| \end_inset |
| |
| and can be used for the weighting filter |
| \begin_inset Formula $W(z)$ |
| \end_inset |
| |
| because it does not need to be available to the decoder. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| To make Speex more robust to packet loss, no prediction is applied on the |
| LSP coefficients prior to quantization. |
| The LSPs are encoded using vector quantization (VQ) with 30 bits for higher |
| quality modes and 18 bits for lower quality. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float figure |
| wide false |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Graphics |
| filename speex_analysis.eps |
| width 35page% |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Frame open-loop analysis |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "cap:Frame-open-loop-analysis" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Section |
| Sub-Frame Analysis-by-Synthesis |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float figure |
| wide false |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Graphics |
| filename speex_abs.eps |
| lyxscale 75 |
| width 40page% |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Analysis-by-synthesis closed-loop optimization on a sub-frame. |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "cap:Sub-frame-AbS" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| The analysis-by-synthesis (AbS) encoder loop is described in Fig. |
| |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:Sub-frame-AbS" |
| |
| \end_inset |
| |
| . |
| There are three main aspects where Speex significantly differs from most |
| other CELP codecs. |
| First, while most recent CELP codecs make use of fractional pitch estimation |
| with a single gain, Speex uses an integer to encode the pitch period, but |
| uses a 3-tap predictor (3 gains). |
| The adaptive codebook contribution |
| \begin_inset Formula $e_{a}[n]$ |
| \end_inset |
| |
| can thus be expressed as: |
| \begin_inset Formula \begin{equation} |
| e_{a}[n]=g_{0}e[n-T-1]+g_{1}e[n-T]+g_{2}e[n-T+1]\label{eq:adaptive-3tap}\end{equation} |
| |
| \end_inset |
| |
| where |
| \begin_inset Formula $g_{0}$ |
| \end_inset |
| |
| , |
| \begin_inset Formula $g_{1}$ |
| \end_inset |
| |
| and |
| \begin_inset Formula $g_{2}$ |
| \end_inset |
| |
| are the jointly quantized pitch gains and |
| \begin_inset Formula $e[n]$ |
| \end_inset |
| |
| is the codec excitation memory. |
| It is worth noting that when the pitch is smaller than the sub-frame size, |
| we repeat the excitation at a period |
| \begin_inset Formula $T$ |
| \end_inset |
| |
| . |
| For example, when |
| \begin_inset Formula $n-T+1\geq0$ |
| \end_inset |
| |
| , we use |
| \begin_inset Formula $n-2T+1$ |
| \end_inset |
| |
| instead. |
| In most modes, the pitch period is encoded with 7 bits in the |
| \begin_inset Formula $\left[17,144\right]$ |
| \end_inset |
| |
| range and the |
| \begin_inset Formula $\beta_{i}$ |
| \end_inset |
| |
| coefficients are vector-quantized using 7 bits at higher bit-rates (15 |
| kbps narrowband and above) and 5 bits at lower bit-rates (11 kbps narrowband |
| and below). |
| \end_layout |
| |
| \begin_layout Standard |
| Many current CELP codecs use moving average (MA) prediction to encode the |
| fixed codebook gain. |
| This provides slightly better coding at the expense of introducing a dependency |
| on previously encoded frames. |
| A second difference is that Speex encodes the fixed codebook gain as the |
| product of the global excitation gain |
| \begin_inset Formula $g_{frame}$ |
| \end_inset |
| |
| with a sub-frame gain corrections |
| \begin_inset Formula $g_{subf}$ |
| \end_inset |
| |
| . |
| This increases robustness to packet loss by eliminating the inter-frame |
| dependency. |
| The sub-frame gain correction is encoded before the fixed codebook is searched |
| (not closed-loop optimized) and uses between 0 and 3 bits per sub-frame, |
| depending on the bit-rate. |
| \end_layout |
| |
| \begin_layout Standard |
| The third difference is that Speex uses sub-vector quantization of the innovatio |
| n (fixed codebook) signal instead of an algebraic codebook. |
| Each sub-frame is divided into sub-vectors of lengths ranging between 5 |
| and 20 samples. |
| Each sub-vector is chosen from a bitrate-dependent codebook and all sub-vectors |
| are concatenated to form a sub-frame. |
| As an example, the 3.95 kbps mode uses a sub-vector size of 20 samples with |
| 32 entries in the codebook (5 bits). |
| This means that the innovation is encoded with 10 bits per sub-frame, or |
| 2000 bps. |
| On the other hand, the 18.2 kbps mode uses a sub-vector size of 5 samples |
| with 256 entries in the codebook (8 bits), so the innovation uses 64 bits |
| per sub-frame, or 12800 bps. |
| |
| \end_layout |
| |
| \begin_layout Section |
| Bit-rates |
| \end_layout |
| |
| \begin_layout Standard |
| So far, no MOS (Mean Opinion Score |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| mean opinion score |
| \end_layout |
| |
| \end_inset |
| |
| ) subjective evaluation has been performed for Speex. |
| In order to give an idea of the quality achievable with it, table |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:quality_vs_bps" |
| |
| \end_inset |
| |
| presents my own subjective opinion on it. |
| It should be noted that different people will perceive the quality differently |
| and that the person that designed the codec often has a bias (one way or |
| another) when it comes to subjective evaluation. |
| Last thing, it should be noted that for most codecs (including Speex) encoding |
| quality sometimes varies depending on the input. |
| Note that the complexity is only approximate (within 0.5 mflops and using |
| the lowest complexity setting). |
| Decoding requires approximately 0.5 mflops |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| complexity |
| \end_layout |
| |
| \end_inset |
| |
| in most modes (1 mflops with perceptual enhancement). |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float table |
| placement h |
| wide true |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="17" columns="5"> |
| <features> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Mode |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Quality |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Bit-rate |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| bit-rate |
| \end_layout |
| |
| \end_inset |
| |
| (bps) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| mflops |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| complexity |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Quality/description |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 250 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| No transmission (DTX) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 2,150 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 6 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Vocoder (mostly for comfort noise) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 2 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 2 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5,950 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 9 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Very noticeable artifacts/noise, good intelligibility |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3-4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 8,000 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 10 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Artifacts/noise sometimes noticeable |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5-6 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 11,000 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 14 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Artifacts usually noticeable only with headphones |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7-8 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 15,000 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 11 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Need good headphones to tell the difference |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 6 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 9 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 18,200 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 17.5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Hard to tell the difference even with good headphones |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 10 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 24,600 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 14.5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Completely transparent for voice, good quality music |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 8 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3,950 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 10.5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Very noticeable artifacts/noise, good intelligibility |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 9 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 10 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 11 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 12 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| reserved |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 13 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Application-defined, interpreted by callback or skipped |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 14 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Speex in-band signaling |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 15 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| - |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Terminator code |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Quality versus bit-rate |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "cap:quality_vs_bps" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Section |
| Perceptual enhancement |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| perceptual enhancement |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| |
| \series bold |
| This section was only valid for version 1.1.12 and earlier. |
| It does not apply to version 1.2-beta1 (and later), for which the new perceptual |
| enhancement is not yet documented. |
| \end_layout |
| |
| \begin_layout Standard |
| This part of the codec only applies to the decoder and can even be changed |
| without affecting inter-operability. |
| For that reason, the implementation provided and described here should |
| only be considered as a reference implementation. |
| The enhancement system is divided into two parts. |
| First, the synthesis filter |
| \begin_inset Formula $S(z)=1/A(z)$ |
| \end_inset |
| |
| is replaced by an enhanced filter: |
| \begin_inset Formula \[ |
| S'(z)=\frac{A\left(z/a_{2}\right)A\left(z/a_{3}\right)}{A\left(z\right)A\left(z/a_{1}\right)}\] |
| |
| \end_inset |
| |
| where |
| \begin_inset Formula $a_{1}$ |
| \end_inset |
| |
| and |
| \begin_inset Formula $a_{2}$ |
| \end_inset |
| |
| depend on the mode in use and |
| \begin_inset Formula $a_{3}=\frac{1}{r}\left(1-\frac{1-ra_{1}}{1-ra_{2}}\right)$ |
| \end_inset |
| |
| with |
| \begin_inset Formula $r=.9$ |
| \end_inset |
| |
| . |
| The second part of the enhancement consists of using a comb filter to enhance |
| the pitch in the excitation domain. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Speex wideband mode (sub-band CELP) |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| wideband |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Speex-wideband-mode" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| For wideband, the Speex approach uses a |
| \emph on |
| q |
| \emph default |
| uadrature |
| \emph on |
| m |
| \emph default |
| irror |
| \emph on |
| f |
| \emph default |
| ilter |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| quadrature mirror filter |
| \end_layout |
| |
| \end_inset |
| |
| (QMF) to split the band in two. |
| The 16 kHz signal is thus divided into two 8 kHz signals, one representing |
| the low band (0-4 kHz), the other the high band (4-8 kHz). |
| The low band is encoded with the narrowband mode described in section |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "sec:Speex-narrowband-mode" |
| |
| \end_inset |
| |
| in such a way that the resulting |
| \begin_inset Quotes eld |
| \end_inset |
| |
| embedded narrowband bit-stream |
| \begin_inset Quotes erd |
| \end_inset |
| |
| can also be decoded with the narrowband decoder. |
| Since the low band encoding has already been described, only the high band |
| encoding is described in this section. |
| \end_layout |
| |
| \begin_layout Section |
| Linear Prediction |
| \end_layout |
| |
| \begin_layout Standard |
| The linear prediction part used for the high-band is very similar to what |
| is done for narrowband. |
| The only difference is that we use only 12 bits to encode the high-band |
| LSP's using a multi-stage vector quantizer (MSVQ). |
| The first level quantizes the 10 coefficients with 6 bits and the error |
| is then quantized using 6 bits, too. |
| \end_layout |
| |
| \begin_layout Section |
| Pitch Prediction |
| \end_layout |
| |
| \begin_layout Standard |
| That part is easy: there's no pitch prediction for the high-band. |
| There are two reasons for that. |
| First, there is usually little harmonic structure in this band (above 4 |
| kHz). |
| Second, it would be very hard to implement since the QMF folds the 4-8 |
| kHz band into 4-0 kHz (reversing the frequency axis), which means that |
| the location of the harmonics is no longer at multiples of the fundamental |
| (pitch). |
| \end_layout |
| |
| \begin_layout Section |
| Excitation Quantization |
| \end_layout |
| |
| \begin_layout Standard |
| The high-band excitation is coded in the same way as for narrowband. |
| |
| \end_layout |
| |
| \begin_layout Section |
| Bit allocation |
| \end_layout |
| |
| \begin_layout Standard |
| For the wideband mode, the entire narrowband frame is packed before the |
| high-band is encoded. |
| The narrowband part of the bit-stream is as defined in table |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:bits-narrowband" |
| |
| \end_inset |
| |
| . |
| The high-band follows, as described in table |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "cap:bits-wideband" |
| |
| \end_inset |
| |
| . |
| For wideband, the mode ID is the same as the Speex quality setting and |
| is defined in table |
| \begin_inset CommandInset ref |
| LatexCommand ref |
| reference "tab:wideband-quality" |
| |
| \end_inset |
| |
| . |
| This also means that a wideband frame may be correctly decoded by a narrowband |
| decoder with the only caveat that if more than one frame is packed in the |
| same packet, the decoder will need to skip the high-band parts in order |
| to sync with the bit-stream. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float table |
| placement h |
| wide true |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="7" columns="7"> |
| <features> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Parameter |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Update rate |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 2 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Wideband bit |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Mode ID |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| LSP |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 12 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 12 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 12 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 12 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Excitation gain |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| sub-frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Excitation VQ |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| sub-frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 20 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 40 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 80 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Total |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| frame |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 36 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 112 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 192 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 352 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Bit allocation for high-band in wideband mode |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "cap:bits-wideband" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Float table |
| placement h |
| wide true |
| sideways false |
| status open |
| |
| \begin_layout Plain Layout |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| begin{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="12" columns="3"> |
| <features> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <column alignment="center" valignment="top" width="0pt"> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Mode/Quality |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Bit-rate |
| \begin_inset Index |
| status collapsed |
| |
| \begin_layout Plain Layout |
| bit-rate |
| \end_layout |
| |
| \end_inset |
| |
| (bps) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Quality/description |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 0 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3,950 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Barely intelligible (mostly for comfort noise) |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 1 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5,750 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Very noticeable artifacts/noise, poor intelligibility |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 2 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7,750 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Very noticeable artifacts/noise, good intelligibility |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 3 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 9,800 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Artifacts/noise sometimes annoying |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 4 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 12,800 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Artifacts/noise usually noticeable |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 5 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 16,800 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Artifacts/noise sometimes noticeable |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 6 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 20,600 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Need good headphones to tell the difference |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 7 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 23,800 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Need good headphones to tell the difference |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 8 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 27,800 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Hard to tell the difference even with good headphones |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 9 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 34,200 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Hard to tell the difference even with good headphones |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| <row> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 10 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| 42,200 |
| \end_layout |
| |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \begin_layout Plain Layout |
| Completely transparent for voice, good quality music |
| \end_layout |
| |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| end{center} |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Plain Layout |
| \begin_inset Caption |
| |
| \begin_layout Plain Layout |
| Quality versus bit-rate for the wideband encoder |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "tab:wideband-quality" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset ERT |
| status open |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| clearpage |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset ERT |
| status collapsed |
| |
| \begin_layout Plain Layout |
| |
| |
| \backslash |
| clearpage |
| \end_layout |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| \start_of_appendix |
| Sample code |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Sample-code" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| This section shows sample code for encoding and decoding speech using the |
| Speex API. |
| The commands can be used to encode and decode a file by calling: |
| \family typewriter |
| |
| \begin_inset Newline newline |
| \end_inset |
| |
| % sampleenc in_file.sw | sampledec out_file.sw |
| \family default |
| |
| \begin_inset Newline newline |
| \end_inset |
| |
| where both files are raw (no header) files encoded at 16 bits per sample |
| (in the machine natural endianness). |
| \end_layout |
| |
| \begin_layout Section |
| sampleenc.c |
| \end_layout |
| |
| \begin_layout Standard |
| sampleenc takes a raw 16 bits/sample file, encodes it and outputs a Speex |
| stream to stdout. |
| Note that the packing used is |
| \series bold |
| not |
| \series default |
| compatible with that of speexenc/speexdec. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "sampleenc.c" |
| lstparams "caption={Source code for sampleenc},label={sampleenc-source-code},numbers=left,numberstyle={\\footnotesize}" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Section |
| sampledec.c |
| \end_layout |
| |
| \begin_layout Standard |
| sampledec reads a Speex stream from stdin, decodes it and outputs it to |
| a raw 16 bits/sample file. |
| Note that the packing used is |
| \series bold |
| not |
| \series default |
| compatible with that of speexenc/speexdec. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "sampledec.c" |
| lstparams "caption={Source code for sampledec},label={sampledec-source-code},numbers=left,numberstyle={\\footnotesize}" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Jitter Buffer for Speex |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand lstinputlisting |
| filename "../speexclient/speex_jitter_buffer.c" |
| lstparams "caption={Example of using the jitter buffer for Speex packets},label={example-speex-jitter},numbers=left,numberstyle={\\footnotesize}" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| IETF RTP Profile |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:IETF-draft" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand verbatiminput |
| filename "draft-ietf-avt-rtp-speex-05-tmp.txt" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| Speex License |
| \begin_inset CommandInset label |
| LatexCommand label |
| name "sec:Speex-License" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset include |
| LatexCommand verbatiminput |
| filename "../COPYING" |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset Newpage newpage |
| \end_inset |
| |
| |
| \end_layout |
| |
| \begin_layout Chapter |
| GNU Free Documentation License |
| \end_layout |
| |
| \begin_layout Standard |
| Version 1.1, March 2000 |
| \end_layout |
| |
| \begin_layout Standard |
| Copyright (C) 2000 Free Software Foundation, Inc. |
| 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted |
| to copy and distribute verbatim copies of this license document, but changing |
| it is not allowed. |
| |
| \end_layout |
| |
| \begin_layout Section* |
| 0. |
| PREAMBLE |
| \end_layout |
| |
| \begin_layout Standard |
| The purpose of this License is to make a manual, textbook, or other written |
| document "free" in the sense of freedom: to assure everyone the effective |
| freedom to copy and redistribute it, with or without modifying it, either |
| commercially or noncommercially. |
| Secondarily, this License preserves for the author and publisher a way |
| to get credit for their work, while not being considered responsible for |
| modifications made by others. |
| \end_layout |
| |
| \begin_layout Standard |
| This License is a kind of "copyleft", which means that derivative works |
| of the document must themselves be free in the same sense. |
| It complements the GNU General Public License, which is a copyleft license |
| designed for free software. |
| \end_layout |
| |
| \begin_layout Standard |
| We have designed this License in order to use it for manuals for free software, |
| because free software needs free documentation: a free program should come |
| with manuals providing the same freedoms that the software does. |
| But this License is not limited to software manuals; it can be used for |
| any textual work, regardless of subject matter or whether it is published |
| as a printed book. |
| We recommend this License principally for works whose purpose is instruction |
| or reference. |
| |
| \end_layout |
| |
| \begin_layout Section* |
| 1. |
| APPLICABILITY AND DEFINITIONS |
| \end_layout |
| |
| \begin_layout Standard |
| This License applies to any manual or other work that contains a notice |
| placed by the copyright holder saying it can be distributed under the terms |
| of this License. |
| The "Document", below, refers to any such manual or work. |
| Any member of the public is a licensee, and is addressed as "you". |
| \end_layout |
| |
| \begin_layout Standard |
| A "Modified Version" of the Document means any work containing the Document |
| or a portion of it, either copied verbatim, or with modifications and/or |
| translated into another language. |
| \end_layout |
| |
| \begin_layout Standard |
| A "Secondary Section" is a named appendix or a front-matter section of the |
| Document that deals exclusively with the relationship of the publishers |
| or authors of the Document to the Document's overall subject (or to related |
| matters) and contains nothing that could fall directly within that overall |
| subject. |
| (For example, if the Document is in part a textbook of mathematics, a Secondary |
| Section may not explain any mathematics.) The relationship could be a matter |
| of historical connection with the subject or with related matters, or of |
| legal, commercial, philosophical, ethical or political position regarding |
| them. |
| \end_layout |
| |
| \begin_layout Standard |
| The "Invariant Sections" are certain Secondary Sections whose titles are |
| designated, as being those of Invariant Sections, in the notice that says |
| that the Document is released under this License. |
| \end_layout |
| |
| \begin_layout Standard |
| The "Cover Texts" are certain short passages of text that are listed, as |
| Front-Cover Texts or Back-Cover Texts, in the notice that says that the |
| Document is released under this License. |
| \end_layout |
| |
| \begin_layout Standard |
| A "Transparent" copy of the Document means a machine-readable copy, represented |
| in a format whose specification is available to the general public, whose |
| contents can be viewed and edited directly and straightforwardly with generic |
| text editors or (for images composed of pixels) generic paint programs |
| or (for drawings) some widely available drawing editor, and that is suitable |
| for input to text formatters or for automatic translation to a variety |
| of formats suitable for input to text formatters. |
| A copy made in an otherwise Transparent file format whose markup has been |
| designed to thwart or discourage subsequent modification by readers is |
| not Transparent. |
| A copy that is not "Transparent" is called "Opaque". |
| \end_layout |
| |
| \begin_layout Standard |
| Examples of suitable formats for Transparent copies include plain ASCII |
| without markup, Texinfo input format, LaTeX input format, SGML or XML using |
| a publicly available DTD, and standard-conforming simple HTML designed |
| for human modification. |
| Opaque formats include PostScript, PDF, proprietary formats that can be |
| read and edited only by proprietary word processors, SGML or XML for which |
| the DTD and/or processing tools are not generally available, and the machine-ge |
| nerated HTML produced by some word processors for output purposes only. |
| \end_layout |
| |
| \begin_layout Standard |
| The "Title Page" means, for a printed book, the title page itself, plus |
| such following pages as are needed to hold, legibly, the material this |
| License requires to appear in the title page. |
| For works in formats which do not have any title page as such, "Title Page" |
| means the text near the most prominent appearance of the work's title, |
| preceding the beginning of the body of the text. |
| \end_layout |
| |
| \begin_layout Section* |
| 2. |
| VERBATIM COPYING |
| \end_layout |
| |
| \begin_layout Standard |
| You may copy and distribute the Document in any medium, either commercially |
| or noncommercially, provided that this License, the copyright notices, |
| and the license notice saying this License applies to the Document are |
| reproduced in all copies, and that you add no other conditions whatsoever |
| to those of this License. |
| You may not use technical measures to obstruct or control the reading or |
| further copying of the copies you make or distribute. |
| However, you may accept compensation in exchange for copies. |
| If you distribute a large enough number of copies you must also follow |
| the conditions in section 3. |
| \end_layout |
| |
| \begin_layout Standard |
| You may also lend copies, under the same conditions stated above, and you |
| may publicly display copies. |
| \end_layout |
| |
| \begin_layout Section* |
| 3. |
| COPYING IN QUANTITY |
| \end_layout |
| |
| \begin_layout Standard |
| If you publish printed copies of the Document numbering more than 100, and |
| the Document's license notice requires Cover Texts, you must enclose the |
| copies in covers that carry, clearly and legibly, all these Cover Texts: |
| Front-Cover Texts on the front cover, and Back-Cover Texts on the back |
| cover. |
| Both covers must also clearly and legibly identify you as the publisher |
| of these copies. |
| The front cover must present the full title with all words of the title |
| equally prominent and visible. |
| You may add other material on the covers in addition. |
| Copying with changes limited to the covers, as long as they preserve the |
| title of the Document and satisfy these conditions, can be treated as verbatim |
| copying in other respects. |
| \end_layout |
| |
| \begin_layout Standard |
| If the required texts for either cover are too voluminous to fit legibly, |
| you should put the first ones listed (as many as fit reasonably) on the |
| actual cover, and continue the rest onto adjacent pages. |
| \end_layout |
| |
| \begin_layout Standard |
| If you publish or distribute Opaque copies of the Document numbering more |
| than 100, you must either include a machine-readable Transparent copy along |
| with each Opaque copy, or state in or with each Opaque copy a publicly-accessib |
| le computer-network location containing a complete Transparent copy of the |
| Document, free of added material, which the general network-using public |
| has access to download anonymously at no charge using public-standard network |
| protocols. |
| If you use the latter option, you must take reasonably prudent steps, when |
| you begin distribution of Opaque copies in quantity, to ensure that this |
| Transparent copy will remain thus accessible at the stated location until |
| at least one year after the last time you distribute an Opaque copy (directly |
| or through your agents or retailers) of that edition to the public. |
| \end_layout |
| |
| \begin_layout Standard |
| It is requested, but not required, that you contact the authors of the Document |
| well before redistributing any large number of copies, to give them a chance |
| to provide you with an updated version of the Document. |
| |
| \end_layout |
| |
| \begin_layout Section* |
| 4. |
| MODIFICATIONS |
| \end_layout |
| |
| \begin_layout Standard |
| You may copy and distribute a Modified Version of the Document under the |
| conditions of sections 2 and 3 above, provided that you release the Modified |
| Version under precisely this License, with the Modified Version filling |
| the role of the Document, thus licensing distribution and modification |
| of the Modified Version to whoever possesses a copy of it. |
| In addition, you must do these things in the Modified Version: |
| \end_layout |
| |
| \begin_layout Itemize |
| A. |
| Use in the Title Page (and on the covers, if any) a title distinct from |
| that of the Document, and from those of previous versions (which should, |
| if there were any, be listed in the History section of the Document). |
| You may use the same title as a previous version if the original publisher |
| of that version gives permission. |
| \end_layout |
| |
| \begin_layout Itemize |
| B. |
| List on the Title Page, as authors, one or more persons or entities responsible |
| for authorship of the modifications in the Modified Version, together with |
| at least five of the principal authors of the Document (all of its principal |
| authors, if it has less than five). |
| \end_layout |
| |
| \begin_layout Itemize |
| C. |
| State on the Title page the name of the publisher of the Modified Version, |
| as the publisher. |
| \end_layout |
| |
| \begin_layout Itemize |
| D. |
| Preserve all the copyright notices of the Document. |
| \end_layout |
| |
| \begin_layout Itemize |
| E. |
| Add an appropriate copyright notice for your modifications adjacent to |
| the other copyright notices. |
| \end_layout |
| |
| \begin_layout Itemize |
| F. |
| Include, immediately after the copyright notices, a license notice giving |
| the public permission to use the Modified Version under the terms of this |
| License, in the form shown in the Addendum below. |
| \end_layout |
| |
| \begin_layout Itemize |
| G. |
| Preserve in that license notice the full lists of Invariant Sections and |
| required Cover Texts given in the Document's license notice. |
| \end_layout |
| |
| \begin_layout Itemize |
| H. |
| Include an unaltered copy of this License. |
| \end_layout |
| |
| \begin_layout Itemize |
| I. |
| Preserve the section entitled "History", and its title, and add to it an |
| item stating at least the title, year, new authors, and publisher of the |
| Modified Version as given on the Title Page. |
| If there is no section entitled "History" in the Document, create one stating |
| the title, year, authors, and publisher of the Document as given on its |
| Title Page, then add an item describing the Modified Version as stated |
| in the previous sentence. |
| \end_layout |
| |
| \begin_layout Itemize |
| J. |
| Preserve the network location, if any, given in the Document for public |
| access to a Transparent copy of the Document, and likewise the network |
| locations given in the Document for previous versions it was based on. |
| These may be placed in the "History" section. |
| You may omit a network location for a work that was published at least |
| four years before the Document itself, or if the original publisher of |
| the version it refers to gives permission. |
| \end_layout |
| |
| \begin_layout Itemize |
| K. |
| In any section entitled "Acknowledgements" or "Dedications", preserve the |
| section's title, and preserve in the section all the substance and tone |
| of each of the contributor acknowledgements and/or dedications given therein. |
| \end_layout |
| |
| \begin_layout Itemize |
| L. |
| Preserve all the Invariant Sections of the Document, unaltered in their |
| text and in their titles. |
| Section numbers or the equivalent are not considered part of the section |
| titles. |
| \end_layout |
| |
| \begin_layout Itemize |
| M. |
| Delete any section entitled "Endorsements". |
| Such a section may not be included in the Modified Version. |
| \end_layout |
| |
| \begin_layout Itemize |
| N. |
| Do not retitle any existing section as "Endorsements" or to conflict in |
| title with any Invariant Section. |
| |
| \end_layout |
| |
| \begin_layout Standard |
| If the Modified Version includes new front-matter sections or appendices |
| that qualify as Secondary Sections and contain no material copied from |
| the Document, you may at your option designate some or all of these sections |
| as invariant. |
| To do this, add their titles to the list of Invariant Sections in the Modified |
| Version's license notice. |
| These titles must be distinct from any other section titles. |
| \end_layout |
| |
| \begin_layout Standard |
| You may add a section entitled "Endorsements", provided it contains nothing |
| but endorsements of your Modified Version by various parties--for example, |
| statements of peer review or that the text has been approved by an organization |
| as the authoritative definition of a standard. |
| \end_layout |
| |
| \begin_layout Standard |
| You may add a passage of up to five words as a Front-Cover Text, and a passage |
| of up to 25 words as a Back-Cover Text, to the end of the list of Cover |
| Texts in the Modified Version. |
| Only one passage of Front-Cover Text and one of Back-Cover Text may be |
| added by (or through arrangements made by) any one entity. |
| If the Document already includes a cover text for the same cover, previously |
| added by you or by arrangement made by the same entity you are acting on |
| behalf of, you may not add another; but you may replace the old one, on |
| explicit permission from the previous publisher that added the old one. |
| \end_layout |
| |
| \begin_layout Standard |
| The author(s) and publisher(s) of the Document do not by this License give |
| permission to use their names for publicity for or to assert or imply endorseme |
| nt of any Modified Version. |
| |
| \end_layout |
| |
| \begin_layout Section* |
| 5. |
| COMBINING DOCUMENTS |
| \end_layout |
| |
| \begin_layout Standard |
| You may combine the Document with other documents released under this License, |
| under the terms defined in section 4 above for modified versions, provided |
| that you include in the combination all of the Invariant Sections of all |
| of the original documents, unmodified, and list them all as Invariant Sections |
| of your combined work in its license notice. |
| \end_layout |
| |
| \begin_layout Standard |
| The combined work need only contain one copy of this License, and multiple |
| identical Invariant Sections may be replaced with a single copy. |
| If there are multiple Invariant Sections with the same name but different |
| contents, make the title of each such section unique by adding at the end |
| of it, in parentheses, the name of the original author or publisher of |
| that section if known, or else a unique number. |
| Make the same adjustment to the section titles in the list of Invariant |
| Sections in the license notice of the combined work. |
| \end_layout |
| |
| \begin_layout Standard |
| In the combination, you must combine any sections entitled "History" in |
| the various original documents, forming one section entitled "History"; |
| likewise combine any sections entitled "Acknowledgements", and any sections |
| entitled "Dedications". |
| You must delete all sections entitled "Endorsements." |
| \end_layout |
| |
| \begin_layout Section* |
| 6. |
| COLLECTIONS OF DOCUMENTS |
| \end_layout |
| |
| \begin_layout Standard |
| You may make a collection consisting of the Document and other documents |
| released under this License, and replace the individual copies of this |
| License in the various documents with a single copy that is included in |
| the collection, provided that you follow the rules of this License for |
| verbatim copying of each of the documents in all other respects. |
| \end_layout |
| |
| \begin_layout Standard |
| You may extract a single document from such a collection, and distribute |
| it individually under this License, provided you insert a copy of this |
| License into the extracted document, and follow this License in all other |
| respects regarding verbatim copying of that document. |
| |
| \end_layout |
| |
| \begin_layout Section* |
| 7. |
| AGGREGATION WITH INDEPENDENT WORKS |
| \end_layout |
| |
| \begin_layout Standard |
| A compilation of the Document or its derivatives with other separate and |
| independent documents or works, in or on a volume of a storage or distribution |
| medium, does not as a whole count as a Modified Version of the Document, |
| provided no compilation copyright is claimed for the compilation. |
| Such a compilation is called an "aggregate", and this License does not |
| apply to the other self-contained works thus compiled with the Document, |
| on account of their being thus compiled, if they are not themselves derivative |
| works of the Document. |
| \end_layout |
| |
| \begin_layout Standard |
| If the Cover Text requirement of section 3 is applicable to these copies |
| of the Document, then if the Document is less than one quarter of the entire |
| aggregate, the Document's Cover Texts may be placed on covers that surround |
| only the Document within the aggregate. |
| Otherwise they must appear on covers around the whole aggregate. |
| \end_layout |
| |
| \begin_layout Section* |
| 8. |
| TRANSLATION |
| \end_layout |
| |
| \begin_layout Standard |
| Translation is considered a kind of modification, so you may distribute |
| translations of the Document under the terms of section 4. |
| Replacing Invariant Sections with translations requires special permission |
| from their copyright holders, but you may include translations of some |
| or all Invariant Sections in addition to the original versions of these |
| Invariant Sections. |
| You may include a translation of this License provided that you also include |
| the original English version of this License. |
| In case of a disagreement between the translation and the original English |
| version of this License, the original English version will prevail. |
| \end_layout |
| |
| \begin_layout Section* |
| 9. |
| TERMINATION |
| \end_layout |
| |
| \begin_layout Standard |
| You may not copy, modify, sublicense, or distribute the Document except |
| as expressly provided for under this License. |
| Any other attempt to copy, modify, sublicense or distribute the Document |
| is void, and will automatically terminate your rights under this License. |
| However, parties who have received copies, or rights, from you under this |
| License will not have their licenses terminated so long as such parties |
| remain in full compliance. |
| |
| \end_layout |
| |
| \begin_layout Section* |
| 10. |
| FUTURE REVISIONS OF THIS LICENSE |
| \end_layout |
| |
| \begin_layout Standard |
| The Free Software Foundation may publish new, revised versions of the GNU |
| Free Documentation License from time to time. |
| Such new versions will be similar in spirit to the present version, but |
| may differ in detail to address new problems or concerns. |
| See http://www.gnu.org/copyleft/. |
| \end_layout |
| |
| \begin_layout Standard |
| Each version of the License is given a distinguishing version number. |
| If the Document specifies that a particular numbered version of this License |
| "or any later version" applies to it, you have the option of following |
| the terms and conditions either of that specified version or of any later |
| version that has been published (not as a draft) by the Free Software Foundatio |
| n. |
| If the Document does not specify a version number of this License, you |
| may choose any version ever published (not as a draft) by the Free Software |
| Foundation. |
| \end_layout |
| |
| \begin_layout Standard |
| \begin_inset CommandInset index_print |
| LatexCommand printindex |
| |
| \end_inset |
| |
| |
| \end_layout |
| |
| \end_body |
| \end_document |
