1 ## 5.4\. Audio Recording 2 3 While some of the requirements outlined in this section are listed as SHOULD 4 since Android 4.3, the Compatibility Definition for future versions are planned 5 to change these to MUST. Existing and new Android devices are **STRONGLY 6 RECOMMENDED** to meet these requirements that are listed as SHOULD, or they 7 will not be able to attain Android compatibility when upgraded to the future 8 version. 9 10 ### 5.4.1\. Raw Audio Capture 11 12 If device implementations declare `android.hardware.microphone`, they: 13 14 * [C-1-1] MUST allow capture of raw audio content with the following 15 characteristics: 16 17 * **Format**: Linear PCM, 16-bit 18 * **Sampling rates**: 8000, 11025, 16000, 44100 Hz 19 * **Channels**: Mono 20 21 * [C-1-2] MUST capture at above sample rates without up-sampling. 22 * [C-1-3] MUST include an appropriate anti-aliasing filter when the 23 sample rates given above are captured with down-sampling. 24 * SHOULD allow AM radio and DVD quality capture of raw audio content, which 25 means the following characteristics: 26 27 * **Format**: Linear PCM, 16-bit 28 * **Sampling rates**: 22050, 48000 Hz 29 * **Channels**: Stereo 30 31 If device implementations allow AM radio and DVD quality capture of raw audio 32 content, they: 33 34 * [C-2-1] MUST capture without up-sampling at any ratio higher 35 than 16000:22050 or 44100:48000. 36 * [C-2-2] MUST include an appropriate anti-aliasing filter for any 37 up-sampling or down-sampling. 38 39 ### 5.4.2\. Capture for Voice Recognition 40 41 If device implementations declare `android.hardware.microphone`, they: 42 43 * [C-1-1] MUST capture 44 `android.media.MediaRecorder.AudioSource.VOICE_RECOGNITION` audio source at 45 one of the sampling rates, 44100 and 48000. 46 * [C-1-2] MUST, by default, disable any noise reduction audio processing when 47 recording an audio stream from the `AudioSource.VOICE_RECOGNITION` audio 48 source. 49 * [C-1-3] MUST, by default, disable any automatic gain control when recording 50 an audio stream from the `AudioSource.VOICE_RECOGNITION` audio source. 51 * SHOULD record the voice recognition audio stream with approximately flat 52 amplitude versus frequency characteristics: specifically, 3 dB, from 100 Hz 53 to 4000 Hz. 54 * SHOULD record the voice recognition audio stream with input sensitivity set 55 such that a 90 dB sound power level (SPL) source at 1000 Hz yields RMS of 56 2500 for 16-bit samples. 57 * SHOULD record the voice recognition audio stream so that the PCM amplitude 58 levels linearly track input SPL changes over at least a 30 dB range from -18 59 dB to +12 dB re 90 dB SPL at the microphone. 60 * SHOULD record the voice recognition audio stream with total harmonic 61 distortion (THD) less than 1% for 1 kHz at 90 dB SPL input level at the 62 microphone. 63 64 If device impelementations declare `android.hardware.microphone` and noise 65 suppression (reduction) technologies tuned for speech recognition, they: 66 67 * [C-2-1] MUST allow this audio affect to be controllable with the 68 `android.media.audiofx.NoiseSuppressor` API. 69 * [C-2-2] MUST uniquely identfiy each noise suppression technology 70 implementation via the `AudioEffect.Descriptor.uuid` field. 71 72 ### 5.4.3\. Capture for Rerouting of Playback 73 74 The `android.media.MediaRecorder.AudioSource` class includes the `REMOTE_SUBMIX` 75 audio source. 76 77 If device implementations declare both `android.hardware.audio.output` and 78 `android.hardware.microphone`, they: 79 80 * [C-1-1] MUST properly implement the `REMOTE_SUBMIX` audio source so that 81 when an application uses the `android.media.AudioRecord` API to record from this 82 audio source, it captures a mix of all audio streams except for the following: 83 84 * `AudioManager.STREAM_RING` 85 * `AudioManager.STREAM_ALARM` 86 * `AudioManager.STREAM_NOTIFICATION` 87 88
