Jak wygenerować określoną częstotliwość dźwięku?

Question

Pracuję nad aplikacją dla systemu Android. Chcę generować zakres częstotliwości od 1KHz do 20KHz. czy mimo to generuje dźwięk o określonej częstotliwości.

Answer 1

Znalazłem ten kod z innego wpisu SO. z tego, co mogę powiedzieć, jest nadal trochę powikłany, ale powinno wystarczyć.

public class PlaySound extends Activity { 
    // originally from http://marblemice.blogspot.com/2010/04/generate-and-play-tone-in-android.html 
    // and modified by Steve Pomeroy <steve@staticfree.info> 
    private final int duration = 3; // seconds 
    private final int sampleRate = 8000; 
    private final int numSamples = duration * sampleRate; 
    private final double sample[] = new double[numSamples]; 
    private final double freqOfTone = 440; // hz 

    private final byte generatedSnd[] = new byte[2 * numSamples]; 

    Handler handler = new Handler(); 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 
    } 

    @Override 
    protected void onResume() { 
     super.onResume(); 

     // Use a new tread as this can take a while 
     final Thread thread = new Thread(new Runnable() { 
      public void run() { 
       genTone(); 
       handler.post(new Runnable() { 

        public void run() { 
         playSound(); 
        } 
       }); 
      } 
     }); 
     thread.start(); 
    } 

    void genTone(){ 
     // fill out the array 
     for (int i = 0; i < numSamples; ++i) { 
      sample[i] = Math.sin(2 * Math.PI * i/(sampleRate/freqOfTone)); 
     } 

     // convert to 16 bit pcm sound array 
     // assumes the sample buffer is normalised. 
     int idx = 0; 
     for (final double dVal : sample) { 
      // scale to maximum amplitude 
      final short val = (short) ((dVal * 32767)); 
      // in 16 bit wav PCM, first byte is the low order byte 
      generatedSnd[idx++] = (byte) (val & 0x00ff); 
      generatedSnd[idx++] = (byte) ((val & 0xff00) >>> 8); 

     } 
    } 

    void playSound(){ 
     final AudioTrack audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, 
       sampleRate, AudioFormat.CHANNEL_CONFIGURATION_MONO, 
       AudioFormat.ENCODING_PCM_16BIT, numSamples, 
       AudioTrack.MODE_STATIC); 
     audioTrack.write(generatedSnd, 0, generatedSnd.length); 
     audioTrack.play(); 
    } 
}