InputStream in1 = getResources().openRawResource(R.raw.myfile);
    InputStream in2 = getResources().openRawResource(R.raw.myfile2);

    Wave w1 = new Wave(in1);
    short[] music1 = w1.getSampleAmplitudes();
    in1.close();

    Wave w2 = new Wave(in2);
    short[] music2 = w2.getSampleAmplitudes();
    in2.close();

    byte[] output = new byte[(music1.length > music2.length) ? music2.length
            : music1.length];

    for (int i = 0; i < output.length; i++) {

        float samplef1 = music1[i] / 32768.0f; // 2^7=128
        float samplef2 = music2[i] / 32768.0f;

        float mixed = (samplef1 + samplef2)/2;
        //reduce the volume a bit:
        mixed *= 0.8;
       //hard clipping
        if (mixed > 1.0f)
            mixed = 1.0f;

        if (mixed < -1.0f)
            mixed = -1.0f;

        byte outputSample = (byte) (mixed * 128.0f);
        output[i] = outputSample;

    } // for loop


    File f = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/"+"result.wav");
    if (f.exists()) {
        f.delete();
    }

    FileOutputStream fo = new FileOutputStream(f);

    WaveHeader wh = w2.getWaveHeader();
    MyWaveHeader mwh = new MyWaveHeader((short) wh.getAudioFormat(),
            (short) wh.getChannels(), wh.getSampleRate(),
            (short) wh.getBitsPerSample(), output.length);
    mwh.write(fo);

    fo.write(output);
    fo.flush();
    fo.close();

    // MusicPlayer
    MediaPlayer mp = new MediaPlayer();
    // Listeners
    mp.setOnCompletionListener(new OnCompletionListener() {

        @Override
        public void onCompletion(MediaPlayer mp) {
            // TODO Auto-generated method stub

        }
    }); // Important

    mp.reset();

    mp.setDataSource(Environment.getExternalStorageDirectory().getAbsolutePath() + "/"+"birdbellhigh.wav");
    mp.setAudioStreamType(AudioManager.STREAM_MUSIC);

    mp.prepare();
    mp.start();

     AudioTrack audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
     22050, AudioFormat.CHANNEL_OUT_DEFAULT,
     AudioFormat.ENCODING_PCM_16BIT, output.length,
     AudioTrack.MODE_STREAM);
     audioTrack.play();
     audioTrack.write(output, 0, output.length);