live4ever said:
It would nice if GB could do it directly though.
I'm kinda glad it doesn't

That sort of wave manipulation might be taken for granted these days, but considering GB's purpose, it could add quite a bit of confusion.
You couldn't reverse-wave MIDI trax, for instance. Reversing note-order won't give you the nyob-nyob effect. I think it would be tough to reverse-wave Apple loops within GB - There are certain tempo, info and stress elements that could throw a beat track or instrument track completely out of time, and a beginner could make a real dog's breakfast of it, trying to sync things back up.
So, having a feature that only works on acoustically recorded data, and is faded out for other tracks, is a move away from the 'make music now' simple approach GB is geared to do.
If wave transformations were to be added for all types of trax, GB engineers would have to find a way to 'render' MIDI trax (and its internal sound sources and effects) into a 'recorded' or acoustic track. The major drawback of this is inefficient playback. MIDI trax are cheap on data, and you should be able to load up several layers of MIDI trax on a small system without latency issues. But try and playback several full quality acoustically sampled tracks at the same time in GB, and you're asking for a world of frustration.
Intermediate to high-end composition software like Logic, ProTools, CuBase, etc etc are geared for wave-intensive tasks, and don't require the software overheads GB has in order to make various sound datatypes playable and simple to use.
-Oro