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255 lines
8.0 KiB
255 lines
8.0 KiB
4 months ago
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## 7.8\. Audio
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### 7.8.1\. Microphone
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If device implementations include a microphone, they:
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* [C-1-1] MUST report the `android.hardware.microphone` feature constant.
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* [C-1-2] MUST meet the audio recording requirements in
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[section 5.4](#5_4_audio_recording).
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* [C-1-3] MUST meet the audio latency requirements in
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[section 5.6](#5_6_audio_latency).
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* [SR] Are STRONGLY RECOMMENDED to support near-ultrasound recording as described
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in [section 7.8.3](#7_8_3_near_ultrasound).
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If device implementations omit a microphone, they:
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* [C-2-1] MUST NOT report the `android.hardware.microphone` feature constant.
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* [C-2-2] MUST implement the audio recording API at least as no-ops, per
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[section 7](#7_hardware_compatibility).
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### 7.8.2\. Audio Output
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If device implementations include a speaker or an audio/multimedia output
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port for an audio output peripheral such as a 4 conductor 3.5mm audio jack or
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USB host mode port using [USB audio class](
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https://source.android.com/devices/audio/usb#audioClass), they:
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* [C-1-1] MUST report the `android.hardware.audio.output` feature constant.
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* [C-1-2] MUST meet the audio playback requirements in
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[section 5.5](#5_5_audio_playback).
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* [C-1-3] MUST meet the audio latency requirements in
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[section 5.6](#5_6_audio_latency).
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* [SR] STRONGLY RECOMMENDED to support near-ultrasound playback as described
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in [section 7.8.3](#7_8_3_near_ultrasound).
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If device implementations do not include a speaker or audio output port, they:
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* [C-2-1] MUST NOT report the `android.hardware.audio.output` feature.
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* [C-2-2] MUST implement the Audio Output related APIs as no-ops at least.
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For the purposes of this section, an "output port" is a
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[physical interface](https://en.wikipedia.org/wiki/Computer_port_%28hardware%29)
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such as a 3.5mm audio jack, HDMI, or USB host mode port with USB audio class.
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Support for audio output over radio-based protocols such as Bluetooth,
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WiFi, or cellular network does not qualify as including an "output port".
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#### 7.8.2.1\. Analog Audio Ports
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In order to be compatible with the [headsets and other audio accessories](
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https://source.android.com/devices/accessories/headset/plug-headset-spec)
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using the 3.5mm audio plug across the Android ecosystem, if device
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implementations include one or more analog audio ports, they:
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* [C-SR] Are STRONGLY RECOMMENDED to include at least one of the
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audio port(s) to be a 4 conductor 3.5mm audio jack.
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If device implementations have a 4 conductor 3.5mm audio jack, they:
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* [C-1-1] MUST support audio playback to stereo headphones and stereo headsets
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with a microphone.
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* [C-1-2] MUST support TRRS audio plugs with the CTIA pin-out order.
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* [C-1-3] MUST support the detection and mapping to the keycodes for the
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following 3 ranges of equivalent impedance between the microphone and ground
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conductors on the audio plug:
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* **70 ohm or less**: `KEYCODE_HEADSETHOOK`
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* **210-290 ohm**: `KEYCODE_VOLUME_UP`
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* **360-680 ohm**: `KEYCODE_VOLUME_DOWN`
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* [C-1-4] MUST trigger `ACTION_HEADSET_PLUG` upon a plug insert, but
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only after all contacts on plug are touching their relevant segments
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on the jack.
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* [C-1-5] MUST be capable of driving at least 150mV ± 10% of output voltage on
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a 32 ohm speaker impedance.
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* [C-1-6] MUST have a microphone bias voltage between 1.8V ~ 2.9V.
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* [C-1-7] MUST detect and map to the keycode for the following
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range of equivalent impedance between the microphone and ground conductors
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on the audio plug:
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* **110-180 ohm:** `KEYCODE_VOICE_ASSIST`
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* [C-SR] Are STRONGLY RECOMMENDED to support audio plugs with the OMTP
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pin-out order.
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* [C-SR] Are STRONGLY RECOMMEND to support audio recording from stereo
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headsets with a microphone.
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If device implementations have a 4 conductor 3.5mm audio jack and support a
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microphone, and broadcast the `android.intent.action.HEADSET_PLUG` with the
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extra value microphone set as 1, they:
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* [C-2-1] MUST support the detection of microphone on the plugged in audio
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accessory.
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#### 7.8.2.2\. Digital Audio Ports
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In order to be compatible with the headsets and other audio accessories using
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USB-C connectors and implementing (USB audio class) across the Android ecosystem
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as defined in [Android USB headset specification](https://source.android.com/devices/accessories/headset/usb-device).
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See Section [2.2.1](#2_2_1_hardware) for device-specific requirements.
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### 7.8.3\. Near-Ultrasound
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Near-Ultrasound audio is the 18.5 kHz to 20 kHz band.
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Device implementations:
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* MUST correctly report the support of
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near-ultrasound audio capability via the [AudioManager.getProperty](
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http://developer.android.com/reference/android/media/AudioManager.html#getProperty%28java.lang.String%29)
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API as follows:
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If [`PROPERTY_SUPPORT_MIC_NEAR_ULTRASOUND`](
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http://developer.android.com/reference/android/media/AudioManager.html#PROPERTY_SUPPORT_MIC_NEAR_ULTRASOUND)
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is "true", the following requirements MUST be met by the
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`VOICE_RECOGNITION` and `UNPROCESSED` audio sources:
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* [C-1-1] The microphone's mean power response in the 18.5 kHz to 20 kHz band
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MUST be no more than 15 dB below the response at 2 kHz.
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* [C-1-2] The microphone's unweighted signal to noise ratio over 18.5 kHz to 20 kHz
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for a 19 kHz tone at -26 dBFS MUST be no lower than 50 dB.
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If [`PROPERTY_SUPPORT_SPEAKER_NEAR_ULTRASOUND`](
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http://developer.android.com/reference/android/media/AudioManager.html#PROPERTY_SUPPORT_SPEAKER_NEAR_ULTRASOUND)
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is "true":
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* [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.
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### 7.8.4\. Signal Integrity
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Device implementations:
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* SHOULD provide a glitch-free audio signal path for both input
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and output streams on handheld devices, as defined by zero glitches
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measured during a test of one minute per path.
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Test using [OboeTester]
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(https://github.com/google/oboe/tree/master/apps/OboeTester)
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“Automated Glitch Test”.
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The test requires an [audio loopback dongle]
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(https://source.android.com/devices/audio/latency/loopback),
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used directly in a 3.5mm jack, and/or in combination with a USB-C to 3.5mm adapter.
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All audio output ports SHOULD be tested.
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OboeTester currently supports AAudio paths, so the
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following combinations SHOULD be tested for glitches using AAudio:
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<table>
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<tr>
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<th>Perf Mode
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<th>Sharing
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<th>Out Sample Rate
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<th>In Chans
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<th>Out Chans
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</tr>
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<tr>
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<td>LOW_LATENCY</td>
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<td>EXCLUSIVE</td>
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<td>UNSPECIFIED</td>
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<td>1</td>
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<td>2</td>
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</tr>
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<tr>
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<td>LOW_LATENCY</td>
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<td>EXCLUSIVE</td>
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<td>UNSPECIFIED</td>
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<td>2</td>
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<td>1</td>
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</tr>
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<tr>
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<td>LOW_LATENCY</td>
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<td>SHARED</td>
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<td>UNSPECIFIED</td>
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<td>1</td>
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<td>2</td>
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</tr>
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<tr>
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<td>LOW_LATENCY</td>
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<td>SHARED</td>
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<td>UNSPECIFIED</td>
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<td>2</td>
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<td>1</td>
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</tr>
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<tr>
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<td>NONE</td>
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<td>SHARED</td>
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<td>48000</td>
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<td>1</td>
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<td>2</td>
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</tr>
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<tr>
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<td>NONE</td>
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<td>SHARED</td>
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<td>48000</td>
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<td>2</td>
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<td>1</td>
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</tr>
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<tr>
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<td>NONE</td>
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<td>SHARED</td>
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<td>44100</td>
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<td>1</td>
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<td>2</td>
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</tr>
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<tr>
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<td>NONE</td>
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<td>SHARED</td>
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<td>44100</td>
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<td>2</td>
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<td>1</td>
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</tr>
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<tr>
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<td>NONE</td>
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<td>SHARED</td>
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<td>16000</td>
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<td>1</td>
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<td>2</td>
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</tr>
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<tr>
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<td>NONE</td>
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<td>SHARED</td>
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<td>16000</td>
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<td>2</td>
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<td>1</td>
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</tr>
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</table>
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A reliable stream SHOULD meet the following criteria for Signal to Noise
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Ratio (SNR) and Total Harmonic Distortion (THD) for 2000 Hz sine.
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<table>
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<tr>
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<th>Transducer</th>
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<th>THD</th>
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<th>SNR</th>
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</tr>
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<tr>
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<td>primary built-in speaker, measured using an external reference microphone</td>
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<td>< 3.0%</td>
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<td>>= 50 dB</td>
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</tr>
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<tr>
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<td>primary built-in microphone, measured using an external reference speaker</td>
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<td>< 3.0%</td>
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<td>>= 50 dB</td>
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</tr>
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<tr>
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<td>built-in analog 3.5 mm jacks, tested using loopback adapter</td>
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<td>< 1%</td>
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<td>>= 60 dB</td>
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</tr>
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<tr>
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<td>USB adapters supplied with the phone, tested using loopback adapter</td>
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<td>< 1.0%</td>
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<td>>= 60 dB</td>
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</tr>
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</table>
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