Morgan Neville's affectionate, entertaining, frequently bitter-sweet documentary shines a spotlight on the (largely African-American) backing singers whose precise verbal pyrotechnics have been the magic ingredient in everything from Da Doo Ron Ron to Gimme Shelter.

Investigating the (mostly) unbridgeable gulf between the back and front of the stage, Morgan concludes that talent and stardom may not be intertwined, as each of his interviewees wrestles group dynamics and personal ambition. A sharply cut early montage neatly establishes gospel singing as the bedrock of the blues and beyond, with conversation often slipping spontaneously into song. Springsteen, Stevie Wonder, Bette Midler et al offer insight into the music business while Sting witters about "spirituality", but it's the likes of Darlene Love who are the real stars here. The result is joyous and uplifting enough to make you almost forgive this for beating Joshua Oppenheimer's incomparable The Act of Killing to the best documentary Oscar.