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我使用公式计算分贝double dB = 20 * Math.log10(p/p0);

p = recorder.getMaxAmplitude()/51805.5336;
p0 = 0.0002;

但是这个类所做的是表示声音幅度在 40 到 70 之间的范围内，它很容易达到 70（最大值），只需在设备上敲击我的手指。

final Runnable updater = new Runnable(){
    public void run(){
        updateTv();
    };
};
final Handler mHandler = new Handler();

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    tv = (TextView)findViewById(R.id.textView1);
    tv.setText("Start");
    startRecording();
    if (runner == null)
    { 
        runner = new Thread(){
            public void run()
            {
                while (runner != null)
                {
                    try
                    {
                        Thread.sleep(500);
                        Log.i("Noise", "Tock");
                    } catch (InterruptedException e) { };
                    mHandler.post(updater);
                }
            }
        };
        runner.start();
        Log.d("Noise", "start runner()");
    }
} 
public void onResume()
{
    super.onResume();

}

protected void updateTv() {
    double decibel = Math.rint(100*getAmplitudeEMA())/100;
    tv.setText("" + decibel + " dB");
    AppLog.logString(Double.toString((getAmplitudeEMA())) + " dB");
}

private double getAmplitudeEMA() {
    double p = getAmplitude()/51805.5336;
    double p0 = 0.0002;
    //mEMA = EMA_FILTER * amp + (1.0 - EMA_FILTER) * mEMA;

    double mEMA2 = 20 * Math.log10(p/p0);

    Log.i("MY", "" + recorder.getMaxAmplitude());
    return mEMA2;
} 

private double getAmplitude() {
    if(recorder != null){
    return recorder.getMaxAmplitude(); }
    else
    return 0;
}

private String getFilename(){
    String filepath = Environment.getExternalStorageDirectory().getPath();
    File file = new File(filepath,AUDIO_RECORDER_FOLDER);
    AppLog.logString(filepath);
    if(!file.exists()){
        file.mkdirs();
    }
    AppLog.logString(file.getAbsolutePath() + "/" + System.currentTimeMillis() + file_exts[currentFormat]);
    return (file.getAbsolutePath() + "/" + System.currentTimeMillis() + file_exts[currentFormat]);
}

private void startRecording(){
    recorder = new MediaRecorder();

    recorder.setAudioSource(MediaRecorder.AudioSource.MIC);
    recorder.setOutputFormat(output_formats[currentFormat]);
    recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
    recorder.setOutputFile(getFilename());

    recorder.setOnErrorListener(errorListener);
    recorder.setOnInfoListener(infoListener);

    try {
        recorder.prepare();
        recorder.start();
    } catch (IllegalStateException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
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