The Funk Brothers spent the 1960s in a cramped basement studio at Hitsville U.S.A. in Detroit, playing on more number-one records than the Beatles, the Beach Boys, the Rolling Stones, and Elvis Presley combined, and almost nobody outside the industry knew their names. The film pulls surviving members like bassist Bob Babbitt and pianist Joe Hunter out of that anonymity, mixing their interviews with reenactments of Motown sessions and archival photos of the studio musicians called Studio A, or the Snakepit. Bassist James Jamerson and drummer Benny Benjamin, both dead before the film was made, get reconstructed through the memories of the men who played beside them. The centerpiece is a present-day reunion concert in Detroit, where the Funk Brothers back singers including Joan Osborne, Chaka Khan, Bootsy Collins, and Ben Harper on the songs they originally recorded for Marvin Gaye, the Temptations, and the Supremes. Motown's founder Berry Gordy built a hit factory on their playing and paid them as session workers rather than stars. The film's case is simple: these were the actual sound of Motown, and the credit went elsewhere.