Button sound problem

Hi all,
I have background music on my page and have a button which I want to play a second sound on roll-over but stop this sound on roll-out. It musn’t interfere with the background music. I am new to action script and have typed this in but obviously a small mistake somewhere as nothing happens!

on (rollOver) {
play(reverse_signal);
}
on (rollOut) {
stop(reverse_signal);
}

Any help would be much appreciated.
Bruce