Stop sound with ActionScript

I’ve got a movie where there’s an audio file looping throughout it (across many different scenes) and in the final scene I need it to stop playing at a particular frame. I’ve tried a few different things with ActionScript (2) but haven’t gotten anywhere. I googled what I wanted to do but most of the results involved buttons - I want this sound to stop when I get to a particular frame, and allow the other sounds to continue playing. I figure it’s only a few lines of AS but I don’t know what’s right. Currently I have this:

onClipEvent (enterFrame) {
busInterior.stop(); }

Which doesn’t make the compiler happy (Clip events are permitted only for movie clip instances). I have the audio file in a movie clip at the moment 'cause I read somwhere that that made things easier, and I wasn’t sure that it would work if I just put the name of the MP3 file in anyway.