| ## 5.4\. Audio Recording |
| |
| While some of the requirements outlined in this section are listed as SHOULD |
| since Android 4.3, the Compatibility Definition for future versions are planned |
| to change these to MUST. Existing and new Android devices are **STRONGLY |
| RECOMMENDED** to meet these requirements that are listed as SHOULD, or they |
| will not be able to attain Android compatibility when upgraded to the future |
| version. |
| |
| ### 5.4.1\. Raw Audio Capture and Microphone Information |
| |
| If device implementations declare `android.hardware.microphone`, they: |
| |
| * [C-1-1] MUST allow capture of raw audio content with the following |
| characteristics: |
| |
| * **Format**: Linear PCM, 16-bit |
| * **Sampling rates**: 8000, 11025, 16000, 44100, 48000 Hz |
| * **Channels**: Mono |
| |
| * SHOULD allow capture of raw audio content with the following |
| characteristics: |
| * **Format**: Linear PCM, 16-bit and 24-bit |
| * **Sampling rates**: 8000, 11025, 16000, 22050, 24000, 32000, 44100, |
| 48000 Hz |
| * **Channels**: As many channels as the number of microphones on the |
| device |
| |
| * [C-1-2] MUST capture at above sample rates without up-sampling. |
| * [C-1-3] MUST include an appropriate anti-aliasing filter when the |
| sample rates given above are captured with down-sampling. |
| * SHOULD allow AM radio and DVD quality capture of raw audio content, which |
| means the following characteristics: |
| |
| * **Format**: Linear PCM, 16-bit |
| * **Sampling rates**: 22050, 48000 Hz |
| * **Channels**: Stereo |
| * [C-1-4] MUST honor the [`MicrophoneInfo`]( |
| https://developer.android.com/reference/android/media/MicrophoneInfo) API |
| and properly fill in information for the available microphones on device |
| accessible to the third-party applications via the |
| [`AudioManager.getMicrophones()`]( |
| https://developer.android.com/reference/android/media/AudioManager#getMicrophones%28%29) |
| API, and the currently active microphones which are accessible to the third |
| party applications via the [`AudioRecord.getActiveMicrophones()`]( |
| https://developer.android.com/reference/android/media/AudioRecord#getActiveMicrophones%28%29) |
| and [`MediaRecorder.getActiveMicrophones()`](https://developer.android.com/reference/android/media/MediaRecorder#getActiveMicrophones%28%29) |
| APIs. |
| If device implementations allow AM radio and DVD quality capture of raw audio |
| content, they: |
| |
| * [C-2-1] MUST capture without up-sampling at any ratio higher |
| than 16000:22050 or 44100:48000. |
| * [C-2-2] MUST include an appropriate anti-aliasing filter for any |
| up-sampling or down-sampling. |
| |
| ### 5.4.2\. Capture for Voice Recognition |
| |
| If device implementations declare `android.hardware.microphone`, they: |
| |
| * [C-1-1] MUST capture |
| `android.media.MediaRecorder.AudioSource.VOICE_RECOGNITION` audio source at |
| one of the sampling rates, 44100 and 48000. |
| * [C-1-2] MUST, by default, disable any noise reduction audio processing when |
| recording an audio stream from the `AudioSource.VOICE_RECOGNITION` audio |
| source. |
| * [C-1-3] MUST, by default, disable any automatic gain control when recording |
| an audio stream from the `AudioSource.VOICE_RECOGNITION` audio source. |
| * SHOULD record the voice recognition audio stream with approximately flat |
| amplitude versus frequency characteristics: specifically, ±3 dB, from 100 Hz |
| to 4000 Hz. |
| * SHOULD record the voice recognition audio stream with input sensitivity set |
| such that a 90 dB sound power level (SPL) source at 1000 Hz yields RMS of |
| 2500 for 16-bit samples. |
| * SHOULD record the voice recognition audio stream so that the PCM amplitude |
| levels linearly track input SPL changes over at least a 30 dB range from -18 |
| dB to +12 dB re 90 dB SPL at the microphone. |
| * SHOULD record the voice recognition audio stream with total harmonic |
| distortion (THD) less than 1% for 1 kHz at 90 dB SPL input level at the |
| microphone. |
| |
| If device implementations declare `android.hardware.microphone` and noise |
| suppression (reduction) technologies tuned for speech recognition, they: |
| |
| * [C-2-1] MUST allow this audio effect to be controllable with the |
| `android.media.audiofx.NoiseSuppressor` API. |
| * [C-2-2] MUST uniquely identify each noise suppression technology |
| implementation via the `AudioEffect.Descriptor.uuid` field. |
| |
| ### 5.4.3\. Capture for Rerouting of Playback |
| |
| The `android.media.MediaRecorder.AudioSource` class includes the `REMOTE_SUBMIX` |
| audio source. |
| |
| If device implementations declare both `android.hardware.audio.output` and |
| `android.hardware.microphone`, they: |
| |
| * [C-1-1] MUST properly implement the `REMOTE_SUBMIX` audio source so that |
| when an application uses the `android.media.AudioRecord` API to record from this |
| audio source, it captures a mix of all audio streams except for the following: |
| |
| * `AudioManager.STREAM_RING` |
| * `AudioManager.STREAM_ALARM` |
| * `AudioManager.STREAM_NOTIFICATION` |
| |
| ### 5.4.4\. Acoustic Echo Canceler |
| |
| If device implementations declare `android.hardware.microphone`, they: |
| |
| * SHOULD implement an [Acoustic Echo Canceler](https://en.wikipedia.org/wiki/Echo_suppression_and_cancellation) |
| (AEC) technology tuned for voice communication and applied to the capture path |
| when capturing using `AudioSource.VOICE_COMMUNICATION` |
| |
| If device implementations provides an Acoustic Echo Canceler which is |
| inserted in the capture audio path when `AudioSource.VOICE_COMMUNICATION` |
| is selected, they: |
| |
| * [C-SR] are STRONGLY_RECOMMENDED to declare this via [AcousticEchoCanceler](https://developer.android.com/reference/android/media/audiofx/AcousticEchoCanceler) |
| API method [AcousticEchoCanceler.isAvailable()](https://developer.android.com/reference/android/media/audiofx/AcousticEchoCanceler.html#isAvailable()) |
| * [C-SR] are STRONGLY_RECOMMENDED to allow this audio effect to be |
| controllable with the [AcousticEchoCanceler](https://developer.android.com/reference/android/media/audiofx/AcousticEchoCanceler) |
| API. |
| * [C-SR] are STRONGLY_RECOMMENDED to uniquely identify each AEC technology |
| implementation via the [AudioEffect.Descriptor.uuid](https://developer.android.com/reference/android/media/audiofx/AudioEffect.Descriptor.html#uuid) |
| field. |
| |
| ### 5.4.5\. Concurrent Capture |
| |
| If device implementations declare `android.hardware.microphone`,they MUST |
| implement concurrent capture as described in [this document]( |
| https://developer.android.com/guide/topics/media/sharing-audio-input). Specifically: |
| |
| * [C-1-1] MUST allow concurrent access to microphone by an accessibility |
| service capturing with `AudioSource.VOICE_RECOGNITION` and at least one |
| application capturing with any `AudioSource`. |
| * [C-1-2] MUST allow concurrent access to microphone by a pre-installed |
| application that holds an Assistant role and at least one application |
| capturing with any `AudioSource` except for |
| `AudioSource.VOICE_COMMUNICATION` or `AudioSource.CAMCORDER`. |
| * [C-1-3] MUST silence the audio capture for any other application, except for |
| an accessibility service, while an application is capturing with |
| `AudioSource.VOICE_COMMUNICATION` or `AudioSource.CAMCORDER`. However, when |
| an app is capturing via `AudioSource.VOICE_COMMUNICATION` then another app |
| can capture the voice call if it is a privileged (pre-installed) app with |
| permission `CAPTURE_AUDIO_OUTPUT`. |
| * [C-1-4] If two or more applications are capturing concurrently and if |
| neither app has an UI on top, the one that started capture the most recently |
| receives audio. |
| |
| ### 5.4.6\. Microphone Gain Levels |
| |
| If device implementations declare `android.hardware.microphone`, they: |
| |
| * SHOULD exhibit approximately flat amplitude-versus-frequency |
| characteristics in the mid-frequency range: specifically ±3dB from 100 |
| Hz to 4000 Hz for each and every microphone used to record the voice |
| recognition audio source. |
| * SHOULD set audio input sensitivity such that a 1000 Hz sinusoidal |
| tone source played at 90 dB Sound Pressure Level (SPL) yields a response |
| with RMS of 2500 for 16 bit-samples (or -22.35 dB Full Scale for floating |
| point/double precision samples) for each and every microphone used to |
| record the voice recognition audio source. |
| * [C-SR] are STRONGLY RECOMMENDED to exhibit amplitude levels in the low |
| frequency range: specifically from ±20 dB from 5 Hz to 100 Hz compared |
| to the mid-frequency range for each and every microphone used to record |
| the voice recognition audio source. |
| * [C-SR] are STRONGLY RECOMMENDED to exhibit amplitude levels in the |
| high frequency range: specifically from ±30 dB from 4000 Hz to 22 KHz |
| compared to the mid-frequency range for each and every microphone used |
| to record the voice recognition audio source. |
