| /* ------------------------------------------------------------------ |
| * Copyright (C) 1998-2009 PacketVideo |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either |
| * express or implied. |
| * See the License for the specific language governing permissions |
| * and limitations under the License. |
| * ------------------------------------------------------------------- |
| */ |
| /* |
| |
| Pathname: tns_ar_filter.c |
| |
| ------------------------------------------------------------------------------ |
| REVISION HISTORY |
| |
| Description: Modified from original shareware code |
| |
| Description: Implemented 24-bit fixed point version |
| Optimized C code |
| |
| Description: |
| - Added OVERFLOW_SHIFT_DOWN to avoid overflow. |
| - Increased precision by using the Q format of the LPC coefficient. |
| - Modified interface to add LPC Q format and scratch memory |
| for the state variables. |
| - Added pv_memset to clear state filter |
| - Updated format for comments (to PV standard) |
| - Updated copyright notice |
| |
| Description: |
| - Changed multiplication scheme to increase precision. This |
| works better than older version. |
| |
| Description: |
| - Include log2(order) as a scaling down parameter. |
| |
| Description: |
| Modified to reflect code review comments |
| - misspelled words, extra comments and explicit requirements |
| |
| Description: |
| deleted comment about fix Q format (L 107) |
| |
| Description: Implemented a more efficient version, which eliminated the use |
| of "scratch memory" via introducing a pointer that references the actual |
| output. |
| |
| Description: Removed the parameter "scratch_Int32_buffer" as this space |
| in memory is no longer needed by this function. |
| |
| Description: Removed references to "scratch_Int32_buffer" in the Inputs |
| section. |
| |
| Description: |
| Modified casting to ensure proper operations for different platforms |
| |
| Description: |
| Per code review comment: |
| Eliminated casting to UInt and Int in b_low and b_high, they are |
| redundant and may add unncessary extra cycles in some platforms |
| |
| Description: Updated the SW template to include the full pathname to the |
| source file and a slightly modified copyright header. |
| |
| Description: Changed the order of the unsigned * signed multiply so the |
| casting to Int32 is performed on the unsigned operand. |
| |
| Description: |
| Modified 32 by 16 bit multiplications to avoid unnecessary moves to |
| registers. Also split the code (based on flag direction) to simplify |
| pointer's updates |
| |
| Description: |
| |
| ------------------------------------------------------------------------------ |
| INPUT AND OUTPUT DEFINITIONS |
| |
| Inputs: |
| spec = spectral input to be shaped by the filter. |
| Fixed point format |
| Int32[] |
| length = spec_length |
| |
| spec_length = length of spec array. |
| const Int |
| |
| direction = direction for application of tns filter. |
| +1 filters spectrum from low to high frequencies |
| (first input to filter is spec[0]) |
| -1 filters spectrum from high to low frequencies |
| (first input to filter is spec[spec_length-1]) |
| const Int |
| |
| lpc = array of lpc coefficients, minus lpc[0] which is assumed to be "1" |
| Fixed point format |
| const Int[] |
| length = TNS_MAX_ORDER |
| |
| Q_lpc = Q format for the lpc coeffcients (for max. precision, it assumes |
| that all 16 bits are used) |
| const Int |
| |
| order = order of the TNS filter (Range of 1 - TNS_MAX_ORDER) |
| Int |
| |
| Local Stores/Buffers/Pointers Needed: |
| None |
| |
| Global Stores/Buffers/Pointers Needed: |
| None |
| |
| Outputs: |
| None |
| |
| Pointers and Buffers Modified: |
| spec = contains spectral data after application of TNS filter |
| Int32 array |
| length = spec_length |
| |
| |
| Local Stores Modified: |
| |
| Global Stores Modified: |
| |
| |
| ------------------------------------------------------------------------------ |
| FUNCTION DESCRIPTION |
| |
| A block of spectral data (Int32 spec[]) of length (const Int spec_length) |
| is processed by a simple all-pole filter defined by |
| LPC coefficients passed via (const Int lpc[]) |
| |
| TNS filter equation |
| y(n) = x(n) - lpc(2)*y(n-1) - ... - lpc(order+1)*y(n-order) |
| |
| The filter calculation is performed in place, i.e. the output is passed |
| back to the calling function via (Int32 spec[]) |
| |
| The filter's order is defined by the variable (const Int order) |
| The direction of the filter's application is defined by (const Int inc) |
| |
| ------------------------------------------------------------------------------ |
| REQUIREMENTS |
| |
| This function should match the functionality of the ISO code. |
| The implementation does support filter orders bigger or equal to 1. |
| The size of the spectral coeffcients has to be bigger or equal than 1. |
| |
| ------------------------------------------------------------------------------ |
| REFERENCES |
| |
| (1) ISO/IEC 14496-3:1999(E) |
| Part 3 |
| Subpart 4.6.8 (Temporal Noise Shaping) |
| |
| (2) MPEG-2 NBC Audio Decoder |
| "This software module was originally developed by AT&T, Dolby |
| Laboratories, Fraunhofer Gesellschaft IIS in the course of development |
| of the MPEG-2 NBC/MPEG-4 Audio standard ISO/IEC 13818-7, 14496-1,2 and |
| 3. This software module is an implementation of a part of one or more |
| MPEG-2 NBC/MPEG-4 Audio tools as specified by the MPEG-2 NBC/MPEG-4 |
| Audio standard. ISO/IEC gives users of the MPEG-2 NBC/MPEG-4 Audio |
| standards free license to this software module or modifications thereof |
| for use in hardware or software products claiming conformance to the |
| MPEG-2 NBC/MPEG-4 Audio standards. Those intending to use this software |
| module in hardware or software products are advised that this use may |
| infringe existing patents. The original developer of this software |
| module and his/her company, the subsequent editors and their companies, |
| and ISO/IEC have no liability for use of this software module or |
| modifications thereof in an implementation. Copyright is not released |
| for non MPEG-2 NBC/MPEG-4 Audio conforming products.The original |
| developer retains full right to use the code for his/her own purpose, |
| assign or donate the code to a third party and to inhibit third party |
| from using the code for non MPEG-2 NBC/MPEG-4 Audio conforming products. |
| This copyright notice must be included in all copies or derivative |
| works." |
| Copyright(c)1996. |
| |
| ------------------------------------------------------------------------------ |
| PSEUDO-CODE |
| |
| |
| FOR (i=0; i<order; i++) |
| state[i] = 0; |
| ENDFOR |
| |
| IF (inc == -1) |
| THEN |
| spec = spec + spec_length - 1; |
| ENDIF |
| |
| FOR (i=0; i<spec_length; i++) |
| |
| y = *spec; |
| |
| FOR (j=0; j<order; j++) |
| |
| y -= lpc[j] * state[j]; |
| |
| ENDFOR |
| |
| FOR (j=order-1; j>0; j--) |
| |
| state[j] = state[j-1]; |
| |
| ENDFOR |
| |
| state[0] = y; |
| |
| *spec = y; |
| |
| spec = spec + inc; |
| |
| ENDFOR |
| |
| |
| ------------------------------------------------------------------------------ |
| RESOURCES USED |
| |
| When the code is written for a specific target processor |
| the resources used should be documented below. |
| |
| STACK USAGE: [stack count for this module] + [variable to represent |
| stack usage for each subroutine called] |
| |
| where: [stack usage variable] = stack usage for [subroutine |
| name] (see [filename].ext) |
| |
| DATA MEMORY USED: x words |
| |
| PROGRAM MEMORY USED: x words |
| |
| CLOCK CYCLES: [cycle count equation for this module] + [variable |
| used to represent cycle count for each subroutine |
| called] |
| |
| where: [cycle count variable] = cycle count for [subroutine |
| name] (see [filename].ext) |
| |
| ------------------------------------------------------------------------------ |
| */ |
| |
| /*---------------------------------------------------------------------------- |
| ; INCLUDES |
| ----------------------------------------------------------------------------*/ |
| #include "pv_audio_type_defs.h" |
| #include "e_tns_const.h" |
| #include "tns_ar_filter.h" |
| #include "fxp_mul32.h" |
| |
| /*---------------------------------------------------------------------------- |
| ; MACROS |
| ; Define module specific macros here |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; DEFINES |
| ; Include all pre-processor statements here. Include conditional |
| ; compile variables also. |
| ----------------------------------------------------------------------------*/ |
| #define MASK_LOW16 0xFFFF |
| #define UPPER16 16 |
| |
| /*---------------------------------------------------------------------------- |
| ; LOCAL FUNCTION DEFINITIONS |
| ; Function Prototype declaration |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; LOCAL STORE/BUFFER/POINTER DEFINITIONS |
| ; Variable declaration - defined here and used outside this module |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; EXTERNAL FUNCTION REFERENCES |
| ; Declare functions defined elsewhere and referenced in this module |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES |
| ; Declare variables used in this module but defined elsewhere |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; FUNCTION CODE |
| ----------------------------------------------------------------------------*/ |
| |
| Int tns_ar_filter( |
| Int32 spec[], |
| const Int spec_length, |
| const Int direction, |
| const Int32 lpc[], |
| const Int Q_lpc, |
| const Int order) |
| { |
| |
| Int i; |
| Int j; |
| |
| /* |
| * Multiplication related variables |
| */ |
| |
| Int32 temp; |
| |
| /* |
| * Filter related variables |
| */ |
| Int32 y0; |
| |
| /* |
| * Circular buffer to hold the filter's state |
| * (y[n-1],y[n-2],y[n-3],etc.) |
| * |
| * p_state and p_lpc should take advantage |
| * of any special circular buffer instructions |
| * if this code is hand-optimized in assembly. |
| */ |
| |
| Int32 *p_state = NULL; |
| |
| const Int32 *p_lpc; |
| |
| |
| Int shift_up; |
| Int shift_down_amount; |
| |
| /* |
| * Pointer to the I/O memory space |
| */ |
| Int32 *p_spec = spec; |
| |
| |
| i = 0; |
| j = order; |
| |
| /* |
| * get the power of 2 that is bigger than the order |
| * i is the bit counter and j is modified until exceed |
| * the power of 2 corresponding to TNS_MAX_ORDER |
| */ |
| |
| while (j < 0x010) |
| { |
| j <<= 1; |
| i++; |
| } |
| |
| /* |
| * 5 is the number of bits needed to represent 0x010 |
| * TNS_MAX_ORDER = 20, power of 2 that include 20 is 5 |
| */ |
| shift_down_amount = 4 - i; |
| |
| shift_up = UPPER16 - Q_lpc; |
| |
| /* |
| * shift_down_amount == power of 2 that is bigger than the order - 1 |
| */ |
| |
| shift_down_amount += shift_up; |
| |
| if (direction == -1) |
| { |
| p_spec += spec_length - 1; |
| |
| for (i = order; i != 0; i--) |
| { |
| |
| y0 = *p_spec >> shift_down_amount; |
| |
| p_lpc = lpc; |
| |
| /* 32 by 32 bit multiplication */ |
| for (j = order; j > i; j--) |
| { |
| temp = *p_state++; |
| y0 -= fxp_mul32_Q31(temp, *(p_lpc++)) << shift_up; |
| } |
| |
| /* |
| * Record the output in-place |
| */ |
| p_state = p_spec; |
| *(p_spec--) = y0; |
| |
| } |
| |
| if (spec_length > order) |
| { |
| for (i = (spec_length - order); i != 0; i--) |
| { |
| y0 = *p_spec >> shift_down_amount; |
| |
| p_lpc = &(lpc[0]); |
| |
| /* 32 by 32 bit multiplication */ |
| for (j = order; j != 0; j--) |
| { |
| temp = *p_state++; |
| y0 -= fxp_mul32_Q31(temp, *(p_lpc++)) << shift_up; |
| } |
| |
| /* |
| * Record the output in-place |
| */ |
| p_state = p_spec; |
| *(p_spec--) = y0; |
| |
| } /* END for (i = (spec_length - order); i>0; i--) */ |
| } |
| |
| } |
| else |
| { |
| for (i = order; i != 0; i--) |
| { |
| |
| p_lpc = lpc; |
| |
| y0 = 0; |
| |
| /* 32 by 32 bit multiplication */ |
| for (j = order; j > i; j--) |
| { |
| y0 -= fxp_mul32_Q31(*p_state--, *(p_lpc++)); |
| } |
| |
| p_state = p_spec; |
| /* |
| * Record the output in-place |
| */ |
| *(p_spec) = (*p_spec >> shift_down_amount) + (y0 << shift_up); |
| p_spec++; |
| } |
| |
| if (spec_length > order) |
| { |
| for (i = (spec_length - order); i != 0; i--) |
| { |
| p_lpc = lpc; |
| |
| y0 = 0; |
| |
| /* 32 by 32 bit multiplication */ |
| for (j = order; j != 0; j--) |
| { |
| y0 -= fxp_mul32_Q31(*p_state--, *(p_lpc++)); |
| } |
| |
| p_state = p_spec; |
| /* |
| * Record the output in-place |
| */ |
| *(p_spec) = (*p_spec >> shift_down_amount) + (y0 << shift_up); |
| p_spec++; |
| |
| } /* END for (i = (spec_length - order); i>0; i--) */ |
| } |
| } |
| |
| return(shift_down_amount); |
| |
| |
| } /* tns_ar_filter */ |
