Volume Control for entire app

Question

My current app could probably be thought of as a sound board. There are a few buttons to click on which produce sounds. The sound are on on View Controller. Nested inside that is another View Controller with the settings which will pop up when called. This is where I need to put my volume slider.

To produce the sounds the parent View Controller will create and release an NSObject which uses the AudioToolbox to produce the sound.

This is how I create and release the object.

if( soundClass != nil ){
    [soundClass release];
}
soundClass = [[SoundClass alloc] initWithFileName:fileToPlay];
[soundClass play];

My question is: Can I control the volume throughout the entire app? Or do I have to set up a sound channel for each clip? How would I approach this? Do I have to rethink how I'm creating the sounds?