| ## 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](#5_4_audio_recording). |
| * [C-1-3] MUST meet the audio latency requirements in |
| [section 5.6](#5_6_audio_latency). |
| * [SR] Are STRONGLY RECOMMENDED to support near-ultrasound recording as described |
| in [section 7.8.3](#7_8_3_near_ultrasound). |
| |
| 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_hardware_compatibility). |
| |
| |
| ### 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]( |
| https://source.android.com/devices/audio/usb#audioClass), 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](#5_5_audio_playback). |
| * [C-1-3] MUST meet the audio latency requirements in |
| [section 5.6](#5_6_audio_latency). |
| * [SR] STRONGLY RECOMMENDED to support near-ultrasound playback as described |
| in [section 7.8.3](#7_8_3_near_ultrasound). |
| |
| 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](https://en.wikipedia.org/wiki/Computer_port_%28hardware%29) |
| 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]( |
| https://source.android.com/devices/accessories/headset/plug-headset-spec) |
| 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](https://source.android.com/devices/accessories/headset/usb-device). |
| |
| See Section [2.2.1](#2_2_1_hardware) 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]( |
| http://developer.android.com/reference/android/media/AudioManager.html#getProperty%28java.lang.String%29) |
| API as follows: |
| |
| If [`PROPERTY_SUPPORT_MIC_NEAR_ULTRASOUND`]( |
| http://developer.android.com/reference/android/media/AudioManager.html#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`]( |
| http://developer.android.com/reference/android/media/AudioManager.html#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: |
| |
| <table> |
| <tr> |
| <th>Perf Mode |
| <th>Sharing |
| <th>Out Sample Rate |
| <th>In Chans |
| <th>Out Chans |
| </tr> |
| <tr> |
| <td>LOW_LATENCY</td> |
| <td>EXCLUSIVE</td> |
| <td>UNSPECIFIED</td> |
| <td>1</td> |
| <td>2</td> |
| </tr> |
| <tr> |
| <td>LOW_LATENCY</td> |
| <td>EXCLUSIVE</td> |
| <td>UNSPECIFIED</td> |
| <td>2</td> |
| <td>1</td> |
| </tr> |
| <tr> |
| <td>LOW_LATENCY</td> |
| <td>SHARED</td> |
| <td>UNSPECIFIED</td> |
| <td>1</td> |
| <td>2</td> |
| </tr> |
| <tr> |
| <td>LOW_LATENCY</td> |
| <td>SHARED</td> |
| <td>UNSPECIFIED</td> |
| <td>2</td> |
| <td>1</td> |
| </tr> |
| <tr> |
| <td>NONE</td> |
| <td>SHARED</td> |
| <td>48000</td> |
| <td>1</td> |
| <td>2</td> |
| </tr> |
| <tr> |
| <td>NONE</td> |
| <td>SHARED</td> |
| <td>48000</td> |
| <td>2</td> |
| <td>1</td> |
| </tr> |
| <tr> |
| <td>NONE</td> |
| <td>SHARED</td> |
| <td>44100</td> |
| <td>1</td> |
| <td>2</td> |
| </tr> |
| <tr> |
| <td>NONE</td> |
| <td>SHARED</td> |
| <td>44100</td> |
| <td>2</td> |
| <td>1</td> |
| </tr> |
| <tr> |
| <td>NONE</td> |
| <td>SHARED</td> |
| <td>16000</td> |
| <td>1</td> |
| <td>2</td> |
| </tr> |
| <tr> |
| <td>NONE</td> |
| <td>SHARED</td> |
| <td>16000</td> |
| <td>2</td> |
| <td>1</td> |
| </tr> |
| </table> |
| |
| A reliable stream SHOULD meet the following criteria for Signal to Noise |
| Ratio (SNR) and Total Harmonic Distortion (THD) for 2000 Hz sine. |
| |
| <table> |
| <tr> |
| <th>Transducer</th> |
| <th>THD</th> |
| <th>SNR</th> |
| </tr> |
| <tr> |
| <td>primary built-in speaker, measured using an external reference microphone</td> |
| <td>< 3.0%</td> |
| <td>>= 50 dB</td> |
| </tr> |
| <tr> |
| <td>primary built-in microphone, measured using an external reference speaker</td> |
| <td>< 3.0%</td> |
| <td>>= 50 dB</td> |
| </tr> |
| <tr> |
| <td>built-in analog 3.5 mm jacks, tested using loopback adapter</td> |
| <td>< 1%</td> |
| <td>>= 60 dB</td> |
| </tr> |
| <tr> |
| <td>USB adapters supplied with the phone, tested using loopback adapter</td> |
| <td>< 1.0%</td> |
| <td>>= 60 dB</td> |
| </tr> |
| </table> |
