в AS2 это был просто stop();

[Arif flasher]

Дерзайте

var req:URLRequest = new URLRequest("baku.mp3");
var sound:Sound = new Sound();
var controller:SoundChannel;
 
function soundLoaded(event:Event):void
{
	controller = sound.play();
	controller.stop();
	play_btn.addEventListener(MouseEvent.CLICK, playSound);
	stop_btn.addEventListener(MouseEvent.CLICK, stopSound);
}
 
function playSound(event:MouseEvent):void
{
	controller = sound.play();
}
 
function stopSound(event:MouseEvent):void
{
	controller.stop();
}
 
sound.addEventListener(Event.COMPLETE, soundLoaded);
sound.load(req);