You have lots of option in OS X. I recommend giving Audacity a try. It records, processes, edits and transcodes. And it's free. There are also a zillion VST plug-ins for it, so if Audacity doesn't natively perform the particular kind of filtering/effects generation you're looking for, chances are that someone has already written a plug-in for it.

More info and D/L links at http://www.pure-mac.com/audio.html#audacity