Flash: How to lower background music when other sound effects play? - actionscript-3

Question

I am using sound files from the library, not URLs.
I am making a soundboard and have a button that plays background music. The reason I have a button instead of automatically playing on load is that there are a few different background musics to choose from, each with their own button.
I also have several other buttons that play sounds. I want the background music volume to lower to something like 0.3 while other sounds are playing. I believe I need to create a variable like soundCount that goes up when a sound plays, and decreases when the sound finishes playing (so that if there are multiple sounds playing at once, the background music won't go back to normal until the count is at 0).
What's the best way to set this up? I made the soundCount variable but I'm having trouble creating an event listener for when sound effect finishes playing.

Answer 1

To change the volume of a sound in AS3, you need to use the SoundChannel and SoundTransform classes:
var backgroundMusic:Sound = // Assuming you've loaded a sound
var myChannel:SoundChannel = new SoundChannel();
myChannel = backgroundMusic.play();
var myTransform = new SoundTransform();
myChannel.soundTransform = myTransform;
Keep track of total sounds in the background by incrementing your count during calls to play and decrementing during SOUND_COMPLETE events. Add event listeners to other sounds' channels so they can modify background's volume:
var totalCurrentSounds:int = 0;
otherSoundChannel.addEventListener(Event.SOUND_COMPLETE, otherSoundComplete);
// Make sure this is on a SoundChannel, not the Sound itself.
Finally, modify the SoundTransform's volume member when the count is 0:
function otherSoundComplete(e:Event):void {
totalCurrentSounds--;
if (totalCurrentSounds <= 0)
myTransform.volume = 0.5;
}