v811_spc009/compatibility/cdd/7_hardware-compatibility/7_8_audio.md

7.8. Audio

7.8.1. Microphone

If device implementations include a microphone, they:

• [C-1-1] MUST report the android.hardware.microphone feature constant.
• [C-1-2] MUST meet the audio recording requirements in section 5.4.
• [C-1-3] MUST meet the audio latency requirements in section 5.6.
• [SR] Are STRONGLY RECOMMENDED to support near-ultrasound recording as described in section 7.8.3.

If device implementations omit a microphone, they:

• [C-2-1] MUST NOT report the android.hardware.microphone feature constant.
• [C-2-2] MUST implement the audio recording API at least as no-ops, per section 7.

7.8.2. Audio Output

If device implementations include a speaker or an audio/multimedia output port for an audio output peripheral such as a 4 conductor 3.5mm audio jack or USB host mode port using USB audio class, they:

• [C-1-1] MUST report the android.hardware.audio.output feature constant.
• [C-1-2] MUST meet the audio playback requirements in section 5.5.
• [C-1-3] MUST meet the audio latency requirements in section 5.6.
• [SR] STRONGLY RECOMMENDED to support near-ultrasound playback as described in section 7.8.3.

If device implementations do not include a speaker or audio output port, they:

• [C-2-1] MUST NOT report the android.hardware.audio.output feature.
• [C-2-2] MUST implement the Audio Output related APIs as no-ops at least.

For the purposes of this section, an "output port" is a physical interface such as a 3.5mm audio jack, HDMI, or USB host mode port with USB audio class. Support for audio output over radio-based protocols such as Bluetooth, WiFi, or cellular network does not qualify as including an "output port".

7.8.2.1. Analog Audio Ports

In order to be compatible with the headsets and other audio accessories using the 3.5mm audio plug across the Android ecosystem, if device implementations include one or more analog audio ports, they:

• [C-SR] Are STRONGLY RECOMMENDED to include at least one of the audio port(s) to be a 4 conductor 3.5mm audio jack.

If device implementations have a 4 conductor 3.5mm audio jack, they:

• [C-1-1] MUST support audio playback to stereo headphones and stereo headsets with a microphone.
• [C-1-2] MUST support TRRS audio plugs with the CTIA pin-out order.
• [C-1-3] MUST support the detection and mapping to the keycodes for the following 3 ranges of equivalent impedance between the microphone and ground conductors on the audio plug:
  • 70 ohm or less: KEYCODE_HEADSETHOOK
  • 210-290 ohm: KEYCODE_VOLUME_UP
  • 360-680 ohm: KEYCODE_VOLUME_DOWN
• [C-1-4] MUST trigger ACTION_HEADSET_PLUG upon a plug insert, but only after all contacts on plug are touching their relevant segments on the jack.
• [C-1-5] MUST be capable of driving at least 150mV ± 10% of output voltage on a 32 ohm speaker impedance.
• [C-1-6] MUST have a microphone bias voltage between 1.8V ~ 2.9V.
• [C-1-7] MUST detect and map to the keycode for the following range of equivalent impedance between the microphone and ground conductors on the audio plug:
  • 110-180 ohm: KEYCODE_VOICE_ASSIST
• [C-SR] Are STRONGLY RECOMMENDED to support audio plugs with the OMTP pin-out order.
• [C-SR] Are STRONGLY RECOMMEND to support audio recording from stereo headsets with a microphone.

If device implementations have a 4 conductor 3.5mm audio jack and support a microphone, and broadcast the android.intent.action.HEADSET_PLUG with the extra value microphone set as 1, they:

• [C-2-1] MUST support the detection of microphone on the plugged in audio accessory.

7.8.2.2. Digital Audio Ports

In order to be compatible with the headsets and other audio accessories using USB-C connectors and implementing (USB audio class) across the Android ecosystem as defined in Android USB headset specification.

See Section 2.2.1 for device-specific requirements.

7.8.3. Near-Ultrasound

Near-Ultrasound audio is the 18.5 kHz to 20 kHz band.

Device implementations:

• MUST correctly report the support of near-ultrasound audio capability via the AudioManager.getProperty API as follows:

If PROPERTY_SUPPORT_MIC_NEAR_ULTRASOUND is "true", the following requirements MUST be met by the VOICE_RECOGNITION and UNPROCESSED audio sources:

• [C-1-1] The microphone's mean power response in the 18.5 kHz to 20 kHz band MUST be no more than 15 dB below the response at 2 kHz.
• [C-1-2] The microphone's unweighted signal to noise ratio over 18.5 kHz to 20 kHz for a 19 kHz tone at -26 dBFS MUST be no lower than 50 dB.

If PROPERTY_SUPPORT_SPEAKER_NEAR_ULTRASOUND is "true":

• [C-2-1] The speaker's mean response in 18.5 kHz - 20 kHz MUST be no lower than 40 dB below the response at 2 kHz.

7.8.4. Signal Integrity

Device implementations:

• SHOULD provide a glitch-free audio signal path for both input and output streams on handheld devices, as defined by zero glitches measured during a test of one minute per path. Test using [OboeTester] (https://github.com/google/oboe/tree/master/apps/OboeTester) “Automated Glitch Test”.

The test requires an [audio loopback dongle] (https://source.android.com/devices/audio/latency/loopback), used directly in a 3.5mm jack, and/or in combination with a USB-C to 3.5mm adapter. All audio output ports SHOULD be tested.

OboeTester currently supports AAudio paths, so the following combinations SHOULD be tested for glitches using AAudio:

Perf Mode	Sharing	Out Sample Rate	In Chans	Out Chans
LOW_LATENCY	EXCLUSIVE	UNSPECIFIED	1	2
LOW_LATENCY	EXCLUSIVE	UNSPECIFIED	2	1
LOW_LATENCY	SHARED	UNSPECIFIED	1	2
LOW_LATENCY	SHARED	UNSPECIFIED	2	1
NONE	SHARED	48000	1	2
NONE	SHARED	48000	2	1
NONE	SHARED	44100	1	2
NONE	SHARED	44100	2	1
NONE	SHARED	16000	1	2
NONE	SHARED	16000	2	1

A reliable stream SHOULD meet the following criteria for Signal to Noise Ratio (SNR) and Total Harmonic Distortion (THD) for 2000 Hz sine.

Transducer	THD	SNR
primary built-in speaker, measured using an external reference microphone	< 3.0%	>= 50 dB
primary built-in microphone, measured using an external reference speaker	< 3.0%	>= 50 dB
built-in analog 3.5 mm jacks, tested using loopback adapter	< 1%	>= 60 dB
USB adapters supplied with the phone, tested using loopback adapter	< 1.0%	>= 60 dB