upload android base code part8
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<html devsite>
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<head>
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<title>Configuring Pre-Processing Effects</title>
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<meta name="project_path" value="/_project.yaml" />
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<meta name="book_path" value="/_book.yaml" />
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</head>
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<body>
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<!--
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Copyright 2017 The Android Open Source Project
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<p>The Android platform provides audio effects on supported devices in the
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<a href="http://developer.android.com/reference/android/media/audiofx/package-summary.html">audiofx</a>
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package, which is available for developers to access. For example, the Nexus 10
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supports the following pre-processing effects:</p>
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<ul>
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<li>
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<a href="http://developer.android.com/reference/android/media/audiofx/AcousticEchoCanceler.html">Acoustic
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Echo Cancellation</a></li>
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<li>
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<a href="http://developer.android.com/reference/android/media/audiofx/AutomaticGainControl.html">Automatic Gain Control</a></li>
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<li>
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<a href="http://developer.android.com/reference/android/media/audiofx/NoiseSuppressor.html">Noise
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Suppression</a></li>
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</ul>
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<h2 id=audiosources>Pairing with AudioSources</h2>
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<p>Pre-processing effects are paired with the use case mode in which the
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pre-processing is requested. In Android app development, a use case is referred
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to as an <code>AudioSource</code>; and app developers request to use the
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<code>AudioSource</code> abstraction instead of the actual audio hardware
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device. The Android Audio Policy Manager maps an <code>AudioSource</code> to a
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given capture path configuration (device, gain, pre processing, etc.) according
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to product-specific rules. The following sources are exposed to developers:</p>
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<ul>
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<li><code>android.media.MediaRecorder.AudioSource.CAMCORDER</code></li>
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<li><code>android.media.MediaRecorder.AudioSource.VOICE_COMMUNICATION</code></li>
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<li><code>android.media.MediaRecorder.AudioSource.VOICE_CALL</code></li>
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<li><code>android.media.MediaRecorder.AudioSource.VOICE_DOWNLINK</code></li>
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<li><code>android.media.MediaRecorder.AudioSource.VOICE_UPLINK</code></li>
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<li><code>android.media.MediaRecorder.AudioSource.VOICE_RECOGNITION</code></li>
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<li><code>android.media.MediaRecorder.AudioSource.MIC</code></li>
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<li><code>android.media.MediaRecorder.AudioSource.DEFAULT</code></li>
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</ul>
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<p>The default pre-processing effects applied for each <code>AudioSource</code>
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are specified in the <code>/system/etc/audio_effects.conf</code> file. To
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specify your own default effects for every <code>AudioSource</code>, create a
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<code>/system/vendor/etc/audio_effects.conf</code> file and specify the
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pre-processing effects to turn on. For an example, see the implementation for
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the Nexus 10 in <code>device/samsung/manta/audio_effects.conf</code>.
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AudioEffect instances acquire and release a session when created and destroyed,
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enabling the effects (such as the Loudness Enhancer) to persist throughout the
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duration of the session.</p>
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<p class="warning"><strong>Warning:</strong> For the
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<code>VOICE_RECOGNITION</code> use case, do not enable the noise suppression
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pre-processing effect. It should not be turned on by default when recording from
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this audio source, and you should not enable it in your own audio_effects.conf
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file. Turning on the effect by default will cause the device to fail the
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<a href="/compatibility/index.html"> compatibility requirement</a>
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regardless of whether this was on by default due to configuration file , or the
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audio HAL implementation's default behavior.</p>
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<p>The following example enables pre-processing for the VoIP
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<code>AudioSource</code> and Camcorder <code>AudioSource</code>. By declaring
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the <code>AudioSource</code> configuration in this manner, the framework will
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automatically request from the audio HAL the use of those effects.</p>
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<pre class="devsite-click-to-copy">
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pre_processing {
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voice_communication {
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aec {}
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ns {}
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}
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camcorder {
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agc {}
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}
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}
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</pre>
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<h2 id=tuning>Source tuning</h2>
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<p><code>AudioSource</code> tuning does not have explicit requirements on audio
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gain or audio processing with the exception of voice recognition
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(<code>VOICE_RECOGNITION</code>). Requirements for voice recognition include:</p>
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<ul>
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<li>Flat frequency response (+/- 3dB) from 100Hz to 4kHz</li>
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<li>Close-talk config: 90dB SPL reads RMS of 2500 (16bit samples)</li>
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<li>Level tracks linearly from -18dB to +12dB relative to 90dB SPL</li>
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<li>THD < 1% (90dB SPL in 100 to 4000Hz range)</li>
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<li>Near-ultrasound requirements (for testing, see
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<a href="/compatibility/cts/near-ultrasound.html">Near Ultrasound
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Tests</a>):
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<ul>
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<li>Support for SUPPORT_PROPERTY_MIC_NEAR_ULTRASOUND as defined in section 7.8.3
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of the CDD.</li>
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<li>Support one or both of 44100 or 48000 sampling rates with no band-pass or
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anti-aliasing filters.</li>
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</ul></li>
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<li>Effects/pre-processing must be disabled by default</li>
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</ul>
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<p>Examples of tuning different effects for different sources are:</p>
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<ul>
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<li>Noise Suppressor
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<ul>
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<li>Tuned for wind noise suppressor for <code>CAMCORDER</code></li>
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<li>Tuned for stationary noise suppressor for <code>VOICE_COMMUNICATION</code></li>
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</ul>
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</li>
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<li>Automatic Gain Control
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<ul>
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<li>Tuned for close-talk for <code>VOICE_COMMUNICATION</code> and main phone
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mic</li>
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<li>Tuned for far-talk for <code>CAMCORDER</code></li>
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</ul>
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</li>
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</ul>
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<h2 id="resources">Resources</h2>
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<p>For more information, refer to the following resources:</p>
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<ul>
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<li>Android documentation for
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<a href="http://developer.android.com/reference/android/media/audiofx/package-summary.html">audiofx
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package</a></li>
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<li>Android documentation for
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<a href="http://developer.android.com/reference/android/media/audiofx/NoiseSuppressor.html">Noise
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Suppression audio effect</a></li>
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<li><code>device/samsung/manta/audio_effects.conf</code> file for the Nexus 10</li>
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</ul>
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</body>
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</html>
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