Booming out from the depths of disco in the 1970s was an unmistakable new sound: a danceable beat and bass riff, laid under an exquisitely tight and inventive horn ensemble, all coaxed out by an ultra-hip narrator whose spoken revelations believably proclaimed they came from another planet. The speaker--actually, the rapper--was musical mastermind George Clinton. Under his inspired direction, the groups Parliament and Funkadelic established what he...