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64 lines
3.2 KiB
64 lines
3.2 KiB
4 months ago
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## 5.11\. Capture for Unprocessed
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Android includes support for recording of unprocessed audio via the
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`android.media.MediaRecorder.AudioSource.UNPROCESSED` audio source. In
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OpenSL ES, it can be accessed with the record preset
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`SL_ANDROID_RECORDING_PRESET_UNPROCESSED`.
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If device implementations intent to support unprocessed audio source and make
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it available to third-party apps, they:
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* [C-1-1] MUST report the support through the `android.media.AudioManager`
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property [PROPERTY_SUPPORT_AUDIO_SOURCE_UNPROCESSED](http://developer.android.com/reference/android/media/AudioManager.html#PROPERTY_SUPPORT_AUDIO_SOURCE_UNPROCESSED).
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* [C-1-2] MUST exhibit approximately flat amplitude-versus-frequency
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characteristics in the mid-frequency range: specifically ±10dB from
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100 Hz to 7000 Hz for each and every microphone used to record the unprocessed
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audio source.
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* [C-1-3] MUST exhibit amplitude levels in the low frequency
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range: specifically from ±20 dB from 5 Hz to 100 Hz compared to the
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mid-frequency range for each and every microphone used to record the
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unprocessed audio source.
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* [C-1-4] MUST exhibit amplitude levels in the high frequency
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range: specifically from ±30 dB from 7000 Hz to 22 KHz compared to the
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mid-frequency range for each and every microphone used to record the
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unprocessed audio source.
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* [C-1-5] MUST set audio input sensitivity such that a 1000 Hz sinusoidal
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tone source played at 94 dB Sound Pressure Level (SPL) yields a response with
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RMS of 520 for 16 bit-samples (or -36 dB Full Scale for floating point/double
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precision samples) for each and every microphone used to record the unprocessed
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audio source.
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* [C-1-6] MUST have a signal-to-noise ratio (SNR) at 60 dB or higher for
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each and every microphone used to record the unprocessed audio source.
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(whereas the SNR is measured as the difference between 94 dB SPL and equivalent
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SPL of self noise, A-weighted).
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* [C-1-7] MUST have a total harmonic distortion (THD) less than be less than
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1% for 1 kHZ at 90 dB SPL input level at each and every microphone used to
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record the unprocessed audio source.
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* MUST not have any other signal processing (e.g. Automatic Gain Control,
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High Pass Filter, or Echo cancellation) in the path other than a level
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multiplier to bring the level to desired range. In other words:
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* [C-1-8] If any signal processing is present in the architecture for any
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reason, it MUST be disabled and effectively introduce zero delay or extra
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latency to the signal path.
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* [C-1-9] The level multiplier, while allowed to be on the path, MUST NOT
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introduce delay or latency to the signal path.
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All SPL measurements are made directly next to the microphone under test.
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For multiple microphone configurations, these requirements apply to
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each microphone.
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If device implementations declare `android.hardware.microphone` but do not
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support unprocessed audio source, they:
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* [C-2-1] MUST return `null` for the `AudioManager.getProperty(PROPERTY_SUPPORT_AUDIO_SOURCE_UNPROCESSED)`
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API method, to properly indicate the lack of support.
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* [SR] are still STRONGLY RECOMMENDED to satisfy as many of the requirements
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for the signal path for the unprocessed recording source.
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