From Version 2.0 of Cool Edit, you've been able to apply various effects in real time in Multitrack and listen to how they sound without permanently altering the track they're applied to. The only downside is that it takes up bags of resources on your computer and if you're running too many tracks, you get dropouts and clicks and random shit happening. And you can save the effects applied to those tracks, STILL WITHOUT MAKING PERMANENT CHANGES. Very cool. EQ, compression, reverb etc - you name it.