I`m loading and playing sound like below.

Code:
//SOUND LOAD

var snd:Sound = new Sound();
snd.load(new URLRequest("sound.mp3"));
snd.addEventListener(IOErrorEvent.IO_ERROR, onIOError, false, 0, true);
snd.addEventListener(Event.COMPLETE, onSoundLoadComplete, false, 0, true);

function onIOError(evt:IOErrorEvent):void{
	trace("sound loading error: ",evt.text);
}

function onSoundLoadComplete(evt:Event):void{
	trace("sound loaded");
}

//SOUND PLAY

snd_btn1.addEventListener(MouseEvent.MOUSE_OVER,sndPlay);

function sndPlay(evt:Event):void{
	
	var channel:SoundChannel
	channel = snd.play(); 
}
i would like to have my sound to play only when it`s not already playing.
how can I achieve this?

thank you