After reaching out to each other with mutual beat-geek enthusiasm and a series of by-mail mixtape trades, Madlib and J Dilla formed the kind of musical partnership that would change both artists in significant ways. Champion Sound is a sort of producer-MC handshake where each artist raps over the other’s beats — Dilla going rugged over Madlib’s subterranean haze and Madlib playing it cool amid Dilla’s loping sub-bass. But it’s also a turning point for both producers: after a brief early ’00s phase of avoiding traditional hip-hop for multitracked one-man-band jazz, Madlib sounds re-energized and down for whatever in Dilla’s presence, while Dilla slips free of the MCA handcuffs  to workshop and refine the more experimental, indie-appeal tendencies he’d started showing on Common’s Electric Circus.