They had big voices, “as big as Aretha Franklin’s,” an admirer confesses. But they gave up their dreams, learned to “sacrifice individuality,” to step into the background as Paul Simon, Ray Charles and legions of others took the spotlight. These lesser lights swayed in time to the music and sang backup, a mere “Twenty Feet from Stardom.”

Filmmaker Morgan Neville (“Johnny Cash’s America”) rounds up a couple of generations of singers and gives them their moment in the sun in this revealing study of egos in check, contributions to music history largely unacknowledged.

That’s Merry Clayton, blistering through the chorus, “Rape, murder, it’s just a shot away,” in the Rolling Stones’ apocalyptic “Gimme Shelter.” That was Luther Vandross, among others, in the backup crew performing the chorus on David Bowie’s “Young Americans.”

We meet Darlene Love and Lisa Fischer, Sheryl Crow and Judith Hill, and hear war stories about working with Joe Cocker and Neil Diamond, Michael Jackson and Whitney Houston.

Nothing scandalous, mind you. If Neville’s movie catches a hint of bitterness here and there, that’s to be expected. But tales out of school? No. These ladies were and are professionals.

Some of the lead singers interviewed here — Sting and Mick Jagger, particularly — seem a little sheepish at the roles these women accepted, embarrassed to have buried their talent in the background. Springsteen professes his awe, and Bette Midler appreciates them as peers.

“Twenty Feet” ends, rather anticlimactically, with a recording session, which only reminds you that it doesn’t have the bounce or swagger of the best of these “behind the music” docs (“The Wrecking Crew” packs more comic and musical punch). It’s still a welcome, entertaining and overdue delivery of credit where credit was, and is, due.