How to fade an NSSound object

Question

I've written a cheap & cheerful sound board in for my Mac, and I play the various sounds with NSSound like this:

-(void)play:(NSSound *)soundEffect:(BOOL)stopIfPlaying {
    BOOL wasPlaying = FALSE;

    if([nowPlaying isPlaying])  {
        [nowPlaying stop];
        wasPlaying = TRUE;
    }   

    if(soundEffect != nowPlaying)
    {
        [soundEffect play];
        nowPlaying = soundEffect;
    } else if(soundEffect == nowPlaying && ![nowPlaying isPlaying] && !wasPlaying) {
        [nowPlaying play];
    }
}

Rather than just stop it dead, I'd like it to fade out over a couple of seconds or so.

Answer 1

Something like this perhaps? You probably want a more linear dropoff, but the basic idea is make a loop and sleep the period of time till the next update.

if([nowPlaying isPlaying])  {
    for(int i = 1; i < 100; ++i)
    {
        [nowPlaying setVolume: (1.0 / i)];
        Sleep(20);
    }
    [nowPlaying stop];
    wasPlaying = TRUE;
}

Answer 2

This is the final version of the method:

-(void)play:(NSSound *)soundEffect:(BOOL)stopIfPlaying {
    BOOL wasPlaying = FALSE;

    if([nowPlaying isPlaying]) {
     struct timespec ts;
     ts.tv_sec = 0;
     ts.tv_nsec = 25000000;

     // If the sound effect is the same, fade it out.
     if(soundEffect == nowPlaying)
     {
      for(int i = 1; i < 30; ++i)
      {
       [nowPlaying setVolume: (1.0 / i )];
       nanosleep(&ts, &ts);
      }   
     }

     [nowPlaying stop];
     [nowPlaying setVolume:1];
     wasPlaying = TRUE;
    } 

    if(soundEffect != nowPlaying)
    {
     [soundEffect play];
     nowPlaying = soundEffect;
    } else if(soundEffect == nowPlaying && ![nowPlaying isPlaying] && !wasPlaying) {
     [nowPlaying play];
    }
}

So it only fades out if I pass the same sound in (ie, click the same button), also, I went for nanosleep rather than sleep, as that on has a granularity of 1 second.

I struggled for a while trying to work out why my 200 millisecond delay didn't seem to have any effect, but then 200 NANOseconds isn't really that long is it :-)

Answer 3

I would use NSTimer to avoid blocking the main thread.