Weird popping noise when playing different sounds with different volumes set through OpenAL on the iPhone

I'm using OpenAL sound framework on the iPhone, and I'm setting different volumes on individual sounds. I'm running into a problem where I'm hearing an initial popping/clicking noise when switching from one sound to the next.

It's really noticeable when I have one sound that's got a high volume (1.0) and a second sound that has a low one (0.2). When I hit the loud sound, and then hit the soft sound, I hear the pop/click. But when I go from the soft sound to the loud, I don't notice anything. So the pop/click really happens when switching from loud to soft sounds.

Here's the init sound method:

 - (id) initWithSoundFile:(NSString *)file doesLoop:(BOOL)loops
{
 self = [super init];
 if (self != nil) 
 {  
  if(![self loadSoundFile:file doesLoop:loops])
   {
   debug(@"Failed to load the sound file: %@...", file);
   [self release];
   return nil;
  }
  self.sourceFileName = file;

  //temporary sound queue
  self.temporarySounds = [NSMutableArray array];

  //default volume/pitch
  self.volume = 1.0;
  self.pitch = 1.0;  
  }
 return self;
    }

and here's the play function:

- (BOOL) play
{

 if([self isPlaying]) //see if the base source is busy...
 {
  //if so, create a 开发者_如何学编程new source
  NSUInteger tmpSourceID;
  alGenSources(1, &tmpSourceID);

  //attach the buffer to the source
  alSourcei(tmpSourceID, AL_BUFFER, bufferID);
  alSourcePlay(tmpSourceID);

  //add the sound id to the play queue so we can dispose of it later
  [temporarySounds addObject: [NSNumber numberWithUnsignedInteger:tmpSourceID]];

  //a "callback" for when the sound is done playing +0.1 secs
  [self performSelector:@selector(deleteTemporarySource)
   withObject:nil
   afterDelay:(duration * pitch) + 0.1];

  return ((error = alGetError()) != AL_NO_ERROR);
 }

 //if the base source isn't busy, just use that one...

 alSourcePlay(sourceID);
 return ((error = alGetError()) != AL_NO_ERROR);
    }

and here's the function where i set the volume for each sound immediately after playing (ive tried setting it before playing too):

- (void) setVolume:(ALfloat)newVolume
{
 volume = MAX(MIN(newVolume, 1.0f), 0.0f); //cap to 0-1
 alSourcef(sourceID, AL_GAIN, volume); 

 //now set the volume for any temporary sounds...

 for(NSNumber *tmpSourceID in temporarySounds)
 {
  //tmpSourceID is the source ID for the temporary sound
  alSourcef([tmpSourceID unsignedIntegerValue], AL_GAIN, volume);
 }
   } 

Any help is greatly appreciated as I've tried everything I can think of. I would be so grateful.

All I had to do was use calloc instead of malloc to allocate memory for the OpenAL buffer. Or you could also zero set the memory with memset.

The wierd popping noise went off. It was due to junk memory in my case. That's why it was random too. Hope this helps.

This problem is caused by not calling alSourceStop.

The documentation doesn't really state this, but alSourceStop must be called on a sound source before it can be reused even if the sound had already finished and the AL_SOURCE_STATE parameter of the source is not AL_PLAYING.

I've randomly got to this unaswered question and, finding that the problem was not solved, I'll try to give my answer, even if a long time has passed.

I don't know OpenAL, but it sounds like this is a purely audio problem. It is normal to hear short clicks when you change suddenly the level of the audio, especially from a high value to a low value. For example, if you map directly the volume of the audio to a slider, which value is updated every few ms, you can easily hear clicks and pops when sliding fast the control. What audio software developers do is smoothing the parameter changes with a low pass filter. In your case, I would suggest you to stop the clip after fading it out, and start a new clip by fading it in. The fade time can be as short as 2 ms: it's not audible, and the sound will play just finely.

I wonder if (some versions of) OpenAL can automatically deal with this issue.