我有一個代碼來計算AudioRecord的實時dB幅度.該代碼非常適合計算dB幅度.錄制后,我將其保存到wav文件.現(xiàn)在,我要播放該文件并重新計算dB幅度.但是,我以前無法達到類似的結(jié)果.你能幫我解決這個問題嗎？這是我在錄制和播放時計算dB幅度的代碼.

1,錄音時計算dB幅度

bufferSize = AudioRecord.getMinBufferSize(16000, AudioFormat.CHANNEL_IN_MONO,
            AudioFormat.ENCODING_PCM_16BIT);
record = new AudioRecord(MediaRecorder.AudioSource.VOICE_COMMUNICATION, SAMPLE_RATE, AudioFormat.CHANNEL_IN_MONO,
            AudioFormat.ENCODING_PCM_16BIT, bufferSize);
audioBuffer = new short[bufferSize];
readSize=record.read(audioBuffer, 0, audioBuffer.length);
double amplitude = 0;
double sum=0;
for (int i = 0; i < readSize; i  ) {
     sum  = audioBuffer[i] * audioBuffer[i];
}
amplitude = sum / readSize;
dbAmp=20.0 *Math.log10(amplitude/32767.0);

2.假設(shè)文件輸出為ouput.wav.我使用MediaPlayer播放和計算幅度

String filePath = Environment.getExternalStorageDirectory().getPath()  "/"  "output.wav";
mPlayer = new  MediaPlayer();
mPlayer.setDataSource(filePath);
mPlayer.prepare();
mPlayer.start();
mVisualizerView.link(mPlayer);

其中,mVisualizerView是Visualizer類.該類具有鏈接功能,例如

 public void link(MediaPlayer player)
  {
    // Create the Visualizer object and attach it to our media player.
    mVisualizer = new Visualizer(player.getAudioSessionId());
    mVisualizer.setScalingMode(Visualizer.SCALING_MODE_NORMALIZED);
    mVisualizer.setCaptureSize(Visualizer.getCaptureSizeRange()[1]);
    // Pass through Visualizer data to VisualizerView
    Visualizer.OnDataCaptureListener captureListener = new Visualizer.OnDataCaptureListener()
    {
      @Override
      public void onWaveFormDataCapture(Visualizer visualizer, byte[] bytes,
          int samplingRate)
      {       
        updateVisualizer(bytes);
      }
      @Override
      public void onFftDataCapture(Visualizer visualizer, byte[] bytes,
          int samplingRate)
      {     
        updateVisualizerFFT(bytes);
      }
    };
    mVisualizer.setDataCaptureListener(captureListener,
        Visualizer.getMaxCaptureRate() / 2, true, true);
    player.setOnCompletionListener(new MediaPlayer.OnCompletionListener()
    {
      @Override
      public void onCompletion(MediaPlayer mediaPlayer)
      {
        mVisualizer.setEnabled(false);
      }
    });
  } 

作為我的任務(wù),我將根據(jù)updateVisualizer或updateVisualizerFFT函數(shù)中的字節(jié)重新計算dbAmp

   public void updateVisualizer(byte[] bytes) {
    dbAmp = computedbAmp(bytes); 
    mBytes = bytes;
    invalidate();
  }
  public void updateVisualizerFFT(byte[] bytes) {
    dbAmp = computedbAmp(bytes);
    mFFTBytes = bytes;
    invalidate();
  }
  public double computedbAmp(byte[] audioData) {
        //System.out.println("::::: audioData :::::" audioData);
      double amplitude = 0;
      for (int i = 0; i < audioData.length/2; i  ) {
          double y = (audioData[i*2] | audioData[i*2 1] << 8) / 32768.0;
          // depending on your endianness:
          // double y = (audioData[i*2]<<8 | audioData[i*2 1]) / 32768.0
          amplitude  = Math.abs(y);
      }
      amplitude = amplitude / audioData.length / 2;
      return amplitude;
    }

目前,我采用某種方法從字節(jié)計算dB幅度.但是,它們是不正確的.您能幫我修復(fù)它或向我建議計算方法嗎？謝謝

我期望的解決方案,例如 Sensor Box for Android

解決方法:

如評論中所提到的,您對兩者沒有使用相同的計算.另外,我認為這兩種方法都不正確.

從第一個示例的代碼中,您似乎正在嘗試計算RMS(即sqrt(sumOfSquares / N)),然后轉(zhuǎn)換為dB.

第二個樣本是sumOfAbs / N,未轉(zhuǎn)換為dB

另一個非常小的問題是,在一種情況下,您需要除以32767,然后再除以32768.兩者都應(yīng)為32768.

對于第一部分,請執(zhí)行以下操作：

double sum=0;
for (int i = 0; i < readSize; i  ) {
    double y = audioBuffer[i] / 32768.0;
    sum  = y * y;
}
double rms = Math.sqrt(sum / readSize);
dbAmp=20.0 *Math.log10(rms);

對于第2部分：

double sum=0;
for (int i = 0; i < audioData.length/2; i  ) {
    double y = (audioData[i*2] | audioData[i*2 1] << 8) / 32768.0;
    sum  = y * y;
}
double rms = Math.sqrt(sum / audioData.length/2);
dbAmp = 20.0*Math.log10(rms);

注意,除了破解字節(jié)數(shù)組外,兩者幾乎完全相同.這應(yīng)該是您找到一種排除該功能的方法的線索,這樣以后您就不會再遇到這種問題了.

編輯：

我忘了提一件事.關(guān)于此問題,存在一些公開辯論,但根據(jù)您的應(yīng)用,您可能希望對dBFS結(jié)果進行正弦校準.我的意思是,正如我所寫的那樣,您將在單個滿量程正弦波上運行計算,您將獲得0.7071(1 / sqrt(2))或-3dBFS的均方根值.如果要使正弦正弦波精確達到零dBFS,則需要將均方根值乘以sqrt(2).