Android的AEC和噪声抑制器在某些设备上不起作用

Question

在开发带有VoIP功能的Android Unity应用程序时，我们发现在某些设备(特别是Galaxy S6)上，麦克风会拾取扬声器输出的声音，导致大量的静态，失真和回声。正因为如此，我开始着手开发一个原生解决方案，以利用Android的一些AEC和NS功能。

我编写了以下测试平台，它在Note 4等一些设备上运行良好。当同样的应用程序在Galaxy S6上运行时，就好像ARC和NS没有得到很好的应用，或者根本没有得到应用。

public class MainActivity extends Activity
{
    private AudioRecord mAudioRecorder = null;
    private AudioTrack mStreamingPlayer = null;
    private Thread playbackThread = null;
    private boolean useVoip = true;
    int bufferSize;
    int chunkSize;
    private AutomaticGainControl agc;
    private NoiseSuppressor suppressor;
    private  AcousticEchoCanceler aec;
    private boolean manuallyAttachEffects = false;
    private void StartRecordingAudio()
    {
        int sampleRate = 44100;
        int channelConfig = AudioFormat.CHANNEL_IN_MONO;
        int audioFormat = AudioFormat.ENCODING_PCM_16BIT;
        chunkSize = AudioRecord.getMinBufferSize(sampleRate, channelConfig, audioFormat);
        bufferSize = chunkSize * 10;
        int audioSource = MediaRecorder.AudioSource.MIC;
        if ( useVoip && !manuallyAttachEffects )
        {
            audioSource = MediaRecorder.AudioSource.VOICE_COMMUNICATION;
        }
        mAudioRecorder = new AudioRecord( audioSource, 
                                        sampleRate,
                                        channelConfig,
                                        audioFormat,
                                        bufferSize );
        if ( useVoip && manuallyAttachEffects )
        {
            SetupVoipEffects( mAudioRecorder.getAudioSessionId() );
        }
        mAudioRecorder.startRecording();
        mStreamingPlayer = new AudioTrack(  AudioManager.STREAM_MUSIC,
                                            sampleRate,
                                            AudioFormat.CHANNEL_OUT_MONO,
                                            audioFormat,
                                            bufferSize,
                                            AudioTrack.MODE_STREAM );
        mStreamingPlayer.play();
        playbackThread = new Thread(new Runnable()
        {
            @Override
            public void run() {
                readAudioData();
            }
        });
        playbackThread.start();
    }
    private void readAudioData()
    {
        Thread thisThread = Thread.currentThread();
        byte[] buffer = new byte[chunkSize];
        while ( !thisThread.isInterrupted() )
        {
            if ( mAudioRecorder == null )
                break;
            int bytesRead = mAudioRecorder.read(buffer, 0, chunkSize);
            if ( bytesRead > 0 )
            {
                if ( mStreamingPlayer == null )
                    break;
                mStreamingPlayer.write(buffer, 0, chunkSize);   
            }
        }
    }
    private void SetupVoipEffects( int sessionId )
    {
        if(AutomaticGainControl.isAvailable())
        {
            agc = AutomaticGainControl.create( sessionId );
            Log.d(LOG_TAG, "AGC is " + (agc.getEnabled()?"enabled":"disabled"));
            if ( !agc.getEnabled() )
            {
                agc.setEnabled(true);
                Log.d(LOG_TAG, "AGC is " + (agc.getEnabled()?"enabled":"disabled" +" after trying to enable"));
            }
        }
        if(NoiseSuppressor.isAvailable())
        {
            suppressor = NoiseSuppressor.create( sessionId );
            Log.d(LOG_TAG, "NS is " + (suppressor.getEnabled()?"enabled":"disabled"));
            if ( !suppressor.getEnabled() )
            {
                suppressor.setEnabled(true);
                Log.d(LOG_TAG, "NS is " + (suppressor.getEnabled()?"enabled":"disabled" +" after trying to disable"));  
            }
        }
        if(AcousticEchoCanceler.isAvailable())
        {
            aec = AcousticEchoCanceler.create( sessionId );
            Log.d(LOG_TAG, "AEC is " + (aec.getEnabled()?"enabled":"disabled"));
            if ( !aec.getEnabled() )
            {
                aec.setEnabled(true);
                Log.d(LOG_TAG, "AEC is " + (aec.getEnabled()?"enabled":"disabled" +" after trying to disable"));
            }
        }
    }
}

我已经尝试了很多事情，如使用VOICE_COMMUNICATION的AudioRecord，使用MIC和手动创建NoiseSuppressor和AcousticEchoCanceller，禁用/启用NuPlayer/AwesomePlayer，等等。设备显示支持并启用了AEC，但它似乎并没有发生。当使用耳机或使用手机而不是扬声器时，这个问题就完全消失了(所以麦克风不能接收扬声器的声音)。是我忽略了什么重要的东西，还是有可能有一个bug要报告?

如果AEC和NS在其他设备上不能完美运行，我不会怀疑。

Answer 1

这是Android的一个已知问题。硬件AEC是不可靠的，并且没有被许多硬件实现/支持，即使它们另有报告。我建议在部署硬件AEC的同时也部署软件AEC，以使该特性在软件中更加稳定。唯一的问题是软件AEC不是那么容易正确地完成，所以要准备好大量的测试。