如何获取android设备上向MIC吹气时的振幅

如何获取android设备中向MIC吹气时的振幅。

MediaRecorder recorder = new MediaRecorder();
   recorder.setAudioSource(MediaRecorder.AudioSource.MIC);

   Timer timer = new Timer();
   timer.scheduleAtFixedRate(new RecorderTask(recorder), 0, 1000);

private class RecorderTask extends TimerTask {
private MediaRecorder recorder;

public RecorderTask(MediaRecorder recorder) {
    this.recorder = recorder;
}

public void run() {
    Log.v("", "amplitude is" + recorder.getMaxAmplitude());
}
}

我收到错误：

ERROR/AndroidRuntime(20927): Caused by: java.lang.RuntimeException: setAudioSource failed.
ERROR/AndroidRuntime(20927): at android.media.MediaRecorder.setAudioSource(Native Method)

public boolean isBlowing()
    {
        boolean recorder=true;

        int minSize = AudioRecord.getMinBufferSize(8000,AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT);
        AudioRecord ar = new AudioRecord(MediaRecorder.AudioSource.MIC, 8000,AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT,minSize);


        short[] buffer = new short[minSize];

        ar.startRecording();
        while(recorder)
        {

            ar.read(buffer, 0, minSize);
            for (short s : buffer) 
            {
                if (Math.abs(s) > 27000)   //DETECT VOLUME (IF I BLOW IN THE MIC)
                {
                    blow_value=Math.abs(s);
                    System.out.println("Blow Value="+blow_value);
                    ar.stop();
                    recorder=false;

                    return true;

                }

            }
        }
        return false;

    }