android/media/audiofx/AutomaticGainControl.java

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.media.audiofx;

import android.util.Log;

/**
 * Automatic Gain Control (AGC).
 * <p>Automatic Gain Control (AGC) is an audio pre-processor which automatically normalizes the
 * output of the captured signal by boosting or lowering input from the microphone to match a preset
 * level so that the output signal level is virtually constant.
 * AGC can be used by applications where the input signal dynamic range is not important but where
 * a constant strong capture level is desired.
 * <p>An application creates a AutomaticGainControl object to instantiate and control an AGC
 * engine in the audio framework.
 * <p>To attach the AutomaticGainControl to a particular {@link android.media.AudioRecord},
 * specify the audio session ID of this AudioRecord when creating the AutomaticGainControl.
 * The audio session is retrieved by calling
 * {@link android.media.AudioRecord#getAudioSessionId()} on the AudioRecord instance.
 * <p>On some devices, an AGC can be inserted by default in the capture path by the platform
 * according to the {@link android.media.MediaRecorder.AudioSource} used. The application should
 * call AutomaticGainControl.getEnable() after creating the AGC to check the default AGC activation
 * state on a particular AudioRecord session.
 * <p>See {@link android.media.audiofx.AudioEffect} class for more details on
 * controlling audio effects.
 */

public class AutomaticGainControl extends AudioEffect {

    private final static String TAG = "AutomaticGainControl";

    /**
     * Checks if the device implements automatic gain control.
     * @return true if the device implements automatic gain control, false otherwise.
     */
    public static boolean isAvailable() {
        return AudioEffect.isEffectTypeAvailable(AudioEffect.EFFECT_TYPE_AGC);
    }

    /**
     * Creates an AutomaticGainControl and attaches it to the AudioRecord on the audio
     * session specified.
     * @param audioSession system wide unique audio session identifier. The AutomaticGainControl
     * will be applied to the AudioRecord with the same audio session.
     * @return AutomaticGainControl created or null if the device does not implement AGC.
     */
    public static AutomaticGainControl create(int audioSession) {
        AutomaticGainControl agc = null;
        try {
            agc = new AutomaticGainControl(audioSession);
        } catch (IllegalArgumentException e) {
            Log.w(TAG, "not implemented on this device "+agc);
        } catch (UnsupportedOperationException e) {
            Log.w(TAG, "not enough resources");
        } catch (RuntimeException e) {
            Log.w(TAG, "not enough memory");
        }
        return agc;
    }

    /**
     * Class constructor.
     * <p> The constructor is not guarantied to succeed and throws the following exceptions:
     * <ul>
     *  <li>IllegalArgumentException is thrown if the device does not implement an AGC</li>
     *  <li>UnsupportedOperationException is thrown is the resources allocated to audio
     *  pre-procesing are currently exceeded.</li>
     *  <li>RuntimeException is thrown if a memory allocation error occurs.</li>
     * </ul>
     *
     * @param audioSession system wide unique audio session identifier. The AutomaticGainControl
     * will be applied to the AudioRecord with the same audio session.
     *
     * @throws java.lang.IllegalArgumentException
     * @throws java.lang.UnsupportedOperationException
     * @throws java.lang.RuntimeException
     */
    private AutomaticGainControl(int audioSession)
            throws IllegalArgumentException, UnsupportedOperationException, RuntimeException {
        super(EFFECT_TYPE_AGC, EFFECT_TYPE_NULL, 0, audioSession);
    }
}