var soundReq:URLRequest=new URLRequest("soso.mp3");
var music:Sound=new Sound(soundReq);
var mainChannel:SoundChannel=music.play(0,1);
var st:SoundTransform=new SoundTransform(1,0);
A.addEventListener(MouseEvent.CLICK,999);
function 999(MouseEvent) {
st.volume=0;
SoundMixer.soundTransform=st;
}