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android 端的声音检测程序，实时获取当前周围环境的声压级，也就是平常所说的分贝值

源码

声音采集利用系统的 MediaRecorder

/**
 * 录音
 * @return 是否成功开始录音
 */
public boolean startRecorder(){
    if (myRecAudioFile == null) {
        return false;
    }
    try {
        mMediaRecorder = new MediaRecorder();

        mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
        mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
        mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
        mMediaRecorder.setOutputFile(myRecAudioFile.getAbsolutePath());

        mMediaRecorder.prepare();
        mMediaRecorder.start();
        isRecording = true;
        return true;
    } catch(IOException exception) {
        mMediaRecorder.reset();
        mMediaRecorder.release();
        mMediaRecorder = null;
        isRecording = false ;
        exception.printStackTrace();
    }catch(IllegalStateException e){
        stopRecording();
        e.printStackTrace();
        isRecording = false ;
    }
    return false;
}
  /**
  * 获取声压值
  */
 public float getMaxAmplitude() {
     if (mMediaRecorder != null) {
         try {
             return mMediaRecorder.getMaxAmplitude();
         } catch (IllegalArgumentException e) {
             e.printStackTrace();
             return 0;
         }
     } else {
         return 5;
     }
 }

自定义显示分贝值得大圆盘 View 取名 SoundDiscView

private float scaleWidth, scaleHeight;
private int newWidth, newHeight;
private Matrix mMatrix = new Matrix();
private Bitmap indicatorBitmap;
private Paint paint = new Paint();
static final long  ANIMATION_INTERVAL = 100;


private void init() {
    Bitmap myBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.noise_index);
    int bitmapWidth = myBitmap.getWidth();
    int bitmapHeight = myBitmap.getHeight();
    newWidth = getWidth();
    newHeight = getHeight();
    scaleWidth = ((float) newWidth) /(float) bitmapWidth;  // 获取缩放比例
    scaleHeight = ((float) newHeight) /(float) bitmapHeight;  //获取缩放比例
    mMatrix.postScale(scaleWidth, scaleHeight);   //设置 mMatrix 的缩放比例
    indicatorBitmap = Bitmap.createBitmap(myBitmap, 0, 0, bitmapWidth, bitmapHeight, mMatrix,true);  //获取同等和背景宽高的指针图的 bitmap

    paint = new Paint();
    paint.setTextSize(55);
    paint.setAntiAlias(true);
    paint.setTextAlign(Paint.Align.CENTER);  //抗锯齿
    paint.setColor(Color.WHITE);
}


@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    currentAngle = getAngle(World.dbCount); //获取指针应该显示的角度
    mMatrix.setRotate(getAngle(World.dbCount), newWidth / 2, newHeight * 215 / 460);   //片相对位置
    canvas.drawBitmap(indicatorBitmap, mMatrix, paint);
    postInvalidateDelayed(ANIMATION_INTERVAL);
    canvas.drawText((int)World.dbCount+" DB", newWidth/2,newHeight*36/46, paint); //图片相对位置
}

启动、暂停与关闭

控制的所有操作全部在 MainActivity 里进行的，当启动或者重新进入 activity 时启动分贝仪，启动代码如下：

 @Override
protected void onResume() {
    super.onResume();
    bListener = true;
    File file = FileUtil.createFile("temp.amr"); //创建录音文件
    if (file != null) {
        Log.v("file", "file =" + file.getAbsolutePath());
        startRecord(file);
    } else {
        Toast.makeText(getApplicationContext(), "创建文件失败", Toast.LENGTH_LONG).show();
    }
}

/**
 * 开始记录
 * @param fFile
 */
public void startRecord(File fFile){
    try{
        mRecorder.setMyRecAudioFile(fFile);
        if (mRecorder.startRecorder()) {
            startListenAudio();
        }else{
            Toast.makeText(this, "启动录音失败", Toast.LENGTH_SHORT).show();
        }
    }catch(Exception e){
        Toast.makeText(this, "录音机已被占用", Toast.LENGTH_SHORT).show();
        e.printStackTrace();
    }
}



private void startListenAudio() {
    thread = new Thread(new Runnable() {
        @Override
        public void run() {
            while (isThreadRun) {
                try {
                    if(bListener) {
                        volume = mRecorder.getMaxAmplitude();  //获取声压值
                        if(volume > 0 && volume < 1000000) {
                            World.setDbCount(20 * (float)(Math.log10(volume)));  //将声压值转为分贝值
                            soundDiscView.refresh(); //子线程刷新 view，调用了 postInvalidate
                        }
                    }
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                    bListener = false;
                }
            }
        }
    });
    thread.start();
}

startListenAudio 的执行过程就是开启一个线程，每隔一段时间获取分贝值然后刷新大圆盘，这里要注意的是在子线程操作刷新 view 的时候要用 postInvalidate，查看 postInvalidate 的源码发现其原理很简单，它就是 v 用了一个 handler 机制，最终刷新肯定是在主线程的。

当 activity 被 onStop 时我们要停止与关闭录音采集，然后删除采集的文件，操作如下：

/**
 * 停止记录
 */
@Override
protected void onStop() {
    super.onStop();
    bListener = false;
    mRecorder.delete(); //停止记录并删除录音文件
}

 public void delete() {
        stopRecording();
        if (myRecAudioFile != null) {
            myRecAudioFile.delete();
            myRecAudioFile = null;
        }
   }

执行

整个效果还行，但是运行发现指针滑动的太突兀，做个缓慢过度

public static float dbCount = 40;

private static float lastDbCount = dbCount;
private static float min = 0.5f;
private static float value = 0;
public static void setDbCount(float dbValue) {
    if (dbValue > lastDbCount) {
        value = dbValue - lastDbCount > min ? dbValue - lastDbCount : min;
    }else{
        value = dbValue - lastDbCount < -min ? dbValue - lastDbCount : -min;
    }
    dbCount = lastDbCount + value * 0.2f ;
    lastDbCount = dbCount;
}

再次执行，perfect !