The great Wilson Pickett laughs with jubilant pride as he describes how he works the raspy ''corn bread'' sound up from his diaphragm into the timbre of his voice. You can hear him do it in concert in Only the Strong Survive: As he performs ''In the Midnight Hour,'' the sheer gritty wallop of the song -- the beat, the heat, the corn bread -- is even more powerful than you remember it.
Few would claim that Mick Jagger, fit as his booty shaking may be, is greater than he was in 1972, but the aging soul legends in ''Only the Strong Survive'' perform with a ferocity and funk that, in many cases, has only been amplified by the hard depths of their experience. Directed by Chris Hegedus and D.A. Pennebaker, the movie is a vital musical ramble, showing us where some of soul's founders landed after their moment of pop glory. Sam Moore, of Sam and Dave, describes how he was a druggie living in a Times Square flophouse in the early '70s. Later, he performs ''When Something Is Wrong With My Baby,'' and his fall, and recovery, is right there in the heartbreaking empathy of his croon. ''Only the Strong Survive'' doesn't have a lot of structural unity, yet when you're listening to someone like Moore, or to Memphis ''king'' Rufus Thomas doing ''Walking the Dog'' with a bawdy wink that belies his 82 years, it's one of the happiest movies around.