| I put it this way - people often compress a signal so the whole thing can be turned up, and the quiet bits are louder. Expanders can kind of turn up the really quiet bits and leave the 'louder' transients as they are - or you could squash that top bit as well. maybe not the most technical way to put it but that's how I got taught and it always made sense.
Try it on a damien rice track or something, loads of ultra-quiet bits that could use it without having to squash down the loudest points and using make up gain.
edit: and of course the other way, as a different style of gate as described above |