CODEWITHSUNDEEP
androidaudioaudiotrack
meeeee
meeeee

Reputation: 2939

Converting mono to stereo sound

I am trying to convert a 16bit mono sound to stereo. The sound is stored as a byte array, so to my understanding that means I duplicate two bytes at a time.

enter image description here

Am I doing this right? The code I produced changes the frequency.

EDIT:

I am successfully generating a mono tone and storing it in byte [] generatedSnd

Playing the mono sound (working): 

    AudioTrack audioTrack = null;                                   // Get audio track
    try {
        audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
                sampleRate, AudioFormat.CHANNEL_OUT_MONO,
                AudioFormat.ENCODING_PCM_16BIT, (int)numSamples*2,
                AudioTrack.MODE_STATIC);
        audioTrack.setStereoVolume(0f, 1f);
        audioTrack.write(generatedSnd, 0, generatedSnd.length);     // Load the track
        audioTrack.play();                                          // Play the track
    }
    catch (Exception e){ }

Converting to stereo sound: 

    int monoByteArrayLength = generatedSnd.length;
    byte [] stereoGeneratedSnd = new byte[monoByteArrayLength * 2];

    stereoGeneratedSnd[0] = generatedSnd[0];
    stereoGeneratedSnd[2] = generatedSnd[0];

    for (int x=1; x<monoByteArrayLength; x+=2) {

        stereoGeneratedSnd[x*2-1] = generatedSnd[x];
        stereoGeneratedSnd[x*2+1] = generatedSnd[x];

        if (x+1 < monoByteArrayLength) {
            stereoGeneratedSnd[x*2] = generatedSnd[x+1];
            stereoGeneratedSnd[x*2+2] = generatedSnd[x+1];
        }
    }

    AudioTrack audioTrack = null;                                   // Get audio track
    try {
        audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
                sampleRate, AudioFormat.CHANNEL_OUT_STEREO,
                AudioFormat.ENCODING_PCM_16BIT, (int)numSamples*2,
                AudioTrack.MODE_STATIC);
        audioTrack.setStereoVolume(0f, 1f);
        audioTrack.write(stereoGeneratedSnd, 0, stereoGeneratedSnd.length);     // Load the track
        audioTrack.play();                                          // Play the track
    }
    catch (Exception e){ }

What I am trying to do is play the sound out of only one channel

Upvotes: 2

Views: 4742

Answers (2)

herme5
herme5

Reputation: 423

Is that intentional that you duplicate two bytes at a time ? The stereo mode in 16bit PCM Wave format takes :

DATA[ ] : [1st byte from Chanel 1], [1st byte from Chanel 2], [2nd byte from Chanel 1], [2nd byte from Chanel 2]...

So that if you want to convert mono to stereo, your array should be :

Mono   : 0, 1, 2, 3 ...
Stereo : 0, 0, 1, 1, 2, 2, 3, 3 ...

and if you want only one channel

Stereo : 0, 0, 1, 0, 2, 0, 3, 0 ...

Upvotes: 5

Michael
Michael

Reputation: 58507

The output from your doubling algorithm is 0, 1, 2, 1, 2, 3, 4, 3, 4, 5, 0, 5.

A simpler (and correct) way of doing the doubling would be:

for (int i = 0; i < monoByteArrayLength; i += 2) {
    stereoGeneratedSnd[i*2+0] = generatedSnd[i];
    stereoGeneratedSnd[i*2+1] = generatedSnd[i+1];
    stereoGeneratedSnd[i*2+2] = generatedSnd[i];
    stereoGeneratedSnd[i*2+3] = generatedSnd[i+1];
}

Output: 0, 1, 0, 1, 2, 3, 2, 3, 4, 5, 4, 5

Upvotes: 2

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