private void mute() {
    AudioManager am = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
    am.setStreamMute(AudioManager.STREAM_MUSIC, true);
}

public void unmute() {
      AudioManager am = (AudioManager)getSystemService(Context.AUDIO_SERVICE);
      am.setStreamMute(AudioManager.STREAM_MUSIC, false);
    }