Jeremy Logan Jeremy Logan - 2 months ago 13
Android Question

Playing an arbitrary tone with Android

Is there any way to make Android emit a sound of arbitrary frequency (meaning, I don't want to have pre-recorded sound files)?

I've looked around and ToneGenerator was the only thing I was able to find that was even close, but it seems to only be capable of outputting the standard DTMF tones.

Any ideas?

Answer

I originally found this example code on a blog, but it had some bugs in it that generated some horrendous sounds. I've fixed the bugs and posted the resulting code here. Seems to work well for me!

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_OUT_MONO,
                AudioFormat.ENCODING_PCM_16BIT, generatedSnd.length,
                AudioTrack.MODE_STATIC);
        audioTrack.write(generatedSnd, 0, generatedSnd.length);
        audioTrack.play();
    }
}
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