Key Class Woes

Hi,
I'v e been doing some reasearch on the key class, but I'm confused. Here is my code:

var keyListener:Object = new Object();
keyListener.onKeyDown = function() {
if (Key.isDown(Key.ENTER)) {
_root.my_sound.start(0,0);
_root.gotoAndStop("stop");
}
};

How would I change it so it looks for a key such a j or f instead of enter???