参考文章Android中实时获取音量分贝值详解：http://www.jb51.net/article/64806.htm

public class MediaRecorderDemo { 
  private final String TAG = "MediaRecord"; 
  private MediaRecorder mMediaRecorder; 
  public static final int MAX_LENGTH = 1000 * 60 * 10;// 最大录音时长1000*60*10; 
  private String filePath; 
 
  public MediaRecorderDemo(){ 
    this.filePath = "/dev/null"; 
  } 
 
  public MediaRecorderDemo(File file) { 
    this.filePath = file.getAbsolutePath(); 
  } 
 
  private long startTime; 
  private long endTime; 
 
  /** 
   * 开始录音 使用amr格式 
   * 
   *      录音文件 
   * @return 
   */ 
  public void startRecord() { 
    // 开始录音 
    /* ①Initial：实例化MediaRecorder对象 */ 
    if (mMediaRecorder == null) 
      mMediaRecorder = new MediaRecorder(); 
    try { 
      /* ②setAudioSource/setVedioSource */ 
      mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);// 设置麦克风 
      /* ②设置音频文件的编码：AAC/AMR_NB/AMR_MB/Default 声音的（波形）的采样 */ 
      mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.DEFAULT); 
            /* 
       * ②设置输出文件的格式：THREE_GPP/MPEG-4/RAW_AMR/Default THREE_GPP(3gp格式 
       * ，H263视频/ARM音频编码)、MPEG-4、RAW_AMR(只支持音频且音频编码要求为AMR_NB) 
       */ 
      mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB); 
 
      /* ③准备 */ 
      mMediaRecorder.setOutputFile(filePath); 
      mMediaRecorder.setMaxDuration(MAX_LENGTH); 
      mMediaRecorder.prepare(); 
      /* ④开始 */ 
      mMediaRecorder.start(); 
      // AudioRecord audioRecord. 
      /* 获取开始时间* */ 
      startTime = System.currentTimeMillis(); 
      updateMicStatus(); 
      Log.i("ACTION_START", "startTime" + startTime); 
    } catch (IllegalStateException e) { 
      Log.i(TAG, 
          "call startAmr(File mRecAudioFile) failed!" 
              + e.getMessage()); 
    } catch (IOException e) { 
      Log.i(TAG, 
          "call startAmr(File mRecAudioFile) failed!" 
              + e.getMessage()); 
    } 
  } 
 
  /** 
   * 停止录音 
   * 
   */ 
  public long stopRecord() { 
    if (mMediaRecorder == null) 
      return 0L; 
    endTime = System.currentTimeMillis(); 
    Log.i("ACTION_END", "endTime" + endTime); 
    mMediaRecorder.stop(); 
    mMediaRecorder.reset(); 
    mMediaRecorder.release(); 
    mMediaRecorder = null; 
    Log.i("ACTION_LENGTH", "Time" + (endTime - startTime)); 
    return endTime - startTime; 
  } 
 
  private final Handler mHandler = new Handler(); 
  private Runnable mUpdateMicStatusTimer = new Runnable() { 
    public void run() { 
      updateMicStatus(); 
    } 
  }; 
 
  /** 
   * 更新话筒状态 
   * 
   */ 
  private int BASE = 1; 
  private int SPACE = 100;// 间隔取样时间 
 
  private void updateMicStatus() { 
    if (mMediaRecorder != null) { 
      double ratio = (double)mMediaRecorder.getMaxAmplitude() /BASE; 
      double db = 0;// 分贝 
      if (ratio > 1) 
        db = 20 * Math.log10(ratio); 
      Log.d(TAG,"分贝值："+db); 
      mHandler.postDelayed(mUpdateMicStatusTimer, SPACE); 
    } 
  } 
}