Android includes support for recording of unprocessed audio via the
android.media.MediaRecorder.AudioSource.UNPROCESSED audio source. In OpenSL ES, it can be accessed with the record preset
If device implementations intent to support unprocessed audio source and make it available to third-party apps, they:
[C-1-1] MUST report the support through the
android.media.AudioManager property PROPERTY_SUPPORT_AUDIO_SOURCE_UNPROCESSED.
[C-1-2] MUST exhibit approximately flat amplitude-versus-frequency characteristics in the mid-frequency range: specifically ±10dB from 100 Hz to 7000 Hz for each and every microphone used to record the unprocessed audio source.
[C-1-3] MUST 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 unprocessed audio source.
[C-1-4] MUST exhibit amplitude levels in the high frequency range: specifically from ±30 dB from 7000 Hz to 22 KHz compared to the mid-frequency range for each and every microphone used to record the unprocessed audio source.
[C-1-5] MUST set audio input sensitivity such that a 1000 Hz sinusoidal tone source played at 94 dB Sound Pressure Level (SPL) yields a response with RMS of 520 for 16 bit-samples (or -36 dB Full Scale for floating point/double precision samples) for each and every microphone used to record the unprocessed audio source.
[C-1-6] MUST have a signal-to-noise ratio (SNR) at 60 dB or higher for each and every microphone used to record the unprocessed audio source. (whereas the SNR is measured as the difference between 94 dB SPL and equivalent SPL of self noise, A-weighted).
[C-1-7] MUST have a total harmonic distortion (THD) less than be less than 1% for 1 kHZ at 90 dB SPL input level at each and every microphone used to record the unprocessed audio source.
MUST not have any other signal processing (e.g. Automatic Gain Control, High Pass Filter, or Echo cancellation) in the path other than a level multiplier to bring the level to desired range. In other words:
[C-1-8] If any signal processing is present in the architecture for any reason, it MUST be disabled and effectively introduce zero delay or extra latency to the signal path.
[C-1-9] The level multiplier, while allowed to be on the path, MUST NOT introduce delay or latency to the signal path.
All SPL measurements are made directly next to the microphone under test. For multiple microphone configurations, these requirements apply to each microphone.
If device implementations declare
android.hardware.microphone but do not support unprocessed audio source, they:
AudioManager.getProperty(PROPERTY_SUPPORT_AUDIO_SOURCE_UNPROCESSED)API method, to properly indicate the lack of support.