a "a soundfile processing program for the Macintosh", written by Tom Erbe. It is optimized for the PowerPC (although older versions run on 68k Macs), and thus does all of its various audio processing (like Phase Vocoding, noise reduction, ring modulation, and others), quite quickly.
And best of all, it's free! (it used to be shareware/demoware, but it appears to not be, anymore.) Unfortunately, it is not Free, but who knows? Tom might be open to the idea...
see www.soundhack.com, for more info