http://www.soundonsound.com/sos/nov01/articles/melodyne.aspheres the article on the original
Capabilities
Melodyne is currently a stand-alone application for Mac (a PC version is coming), and its purpose in life is to analyse audio minutely and then process it such that almost everything about it can be altered at will. It can shift the pitch of monophonic audio without changing duration, change duration or tempo with or without changing pitch, and manipulate formants to alter voice or instrument character or to improve the character of shifted audio. It allows you to create harmonies from one vocal, or indeed construct whole new melodies, as well as making vocals and instruments do things they couldn't normally do. It can force audio of different tempos to run at one tempo, quantise audio timing, correct pitching errors across an entire track or one note at a time, superimpose pitch information from one melody onto another without affecting lyrics, alter amplitude, edit transitions between notes, and even alter vibrato. While it usually requires monophonic audio, it works on drum and percussion loops and will also process strummed guitar. Sounds impressive? It does to us...