android - 如何从声音android中找出RPM(每分钟旋转)？

Question

我的目标是通过分析球旋转过程中产生的声音来获得强力球的转速。在Google Play中，有几个应用程序可以通过声音来计算转速和频率，但是每个应用程序都无法找出动力球的转速。我在Google上搜索后发现，“要根据声音计算频率，我们必须使用FFT算法”。

什么是强力球？
强力球旋转并产生声音。
“Powerball®产生的阻力与用户所付出的努力成正比”。

class RecorderThread1 extends Thread {
 private static final String TAG = RecorderThread1.class.getSimpleName();
 public boolean recording; // variable to start or stop recording
 public int frequency; // the public variable that contains the frequency
 private PlaceholderFragment placeHolder;
 private Handler handler;
 private long avgFrequency;
 private int avg = 0;
 private int sampelRateHz = 8000;

 // value "heard", it is updated continually while
 // the thread is running.

 public RecorderThread1(PlaceholderFragment placeHolder) {
  this.placeHolder = placeHolder;
 }

 @Override
 public void run() {
  AudioRecord recorder;
  int numCrossing, p;
  short audioData[];
  int bufferSize;

  bufferSize = AudioRecord.getMinBufferSize(8000,
    AudioFormat.CHANNEL_CONFIGURATION_MONO,
    AudioFormat.ENCODING_PCM_16BIT) * 3; // get the buffer size to
              // use with this audio
              // record

  recorder = new AudioRecord(AudioSource.MIC, 8000,
    AudioFormat.CHANNEL_CONFIGURATION_MONO,
    AudioFormat.ENCODING_PCM_16BIT, bufferSize); // instantiate the
                // AudioRecorder

  recording = true; // variable to use start or stop recording
  audioData = new short[bufferSize]; // short array that pcm data is put
           // into.

  while (recording) { // loop while recording is needed
   if (recorder.getState() == android.media.AudioRecord.STATE_INITIALIZED) // check
                     // to
                     // see
                     // if
                     // the
                     // recorder
                     // has
                     // initialized
                     // yet.
    if (recorder.getRecordingState() == android.media.AudioRecord.RECORDSTATE_STOPPED)
     recorder.startRecording(); // check to see if the Recorder
            // has stopped or is not
            // recording, and make it
            // record.

    else {
     recorder.read(audioData, 0, bufferSize); // read the PCM
                // audio data
                // into the
                // audioData
                // array

     // Now we need to decode the PCM data using the Zero
     // Crossings Method

     numCrossing = 0; // initialize your number of zero crossings
          // to 0
     for (p = 0; p  0 && audioData[p + 1] = 0)
       numCrossing++;
      if (audioData[p + 1] > 0 && audioData[p + 2] = 0)
       numCrossing++;
      if (audioData[p + 2] > 0 && audioData[p + 3] = 0)
       numCrossing++;
      if (audioData[p + 3] > 0 && audioData[p + 4] = 0)
       numCrossing++;
     }// for p

     for (p = (bufferSize / 4) * 4; p  0 && audioData[p + 1] = 0)
       numCrossing++;
     }

     frequency = (8000 / bufferSize) * (numCrossing / 2); // Set
     // the audio Frequency to half the number of zero crossings, times the number of samples our buffersize is per second.

     avgFrequency = avgFrequency + frequency;
     avg++;
     Log.d(TAG, " frequency is " + frequency);
     if (handler == null) {
      handler = new Handler(Looper.getMainLooper());
      handler.postDelayed(runnable, 2000);
     }
     // placeHolder.printFrequency((frequency * 60));

    }// else recorder started

  } // while recording

Answer 1

除非声音是纯正弦波或方波，否则过零的次数将是不可靠的，更高和更低的频率会增加噪声。
您可以在其中找到FFT算法:FFT library in android Sdk
FFT正在计算频带中的功率(如频谱分析仪所显示的)。您应该尝试从强力球声音中查看曲线图像，并确定哪种是处理它的最佳方法(较低的频率峰值，较高的峰值……)。