CDD: Add requirements for microphone gain levels
This is to ensure a consistent user experience when using
an Assistant with voice input across the Android ecosystem.
diff --git a/5_multimedia/5_4_audio-recording.md b/5_multimedia/5_4_audio-recording.md
index 8627298..d63789d 100644
@@ -159,4 +159,26 @@
* [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.
\ No newline at end of file
+ receives audio.
+### 5.4.7\. 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.