On classic gospel, R&B, Rock ‘n’ Roll, soul and even white pop, it is pointed out, what one knows and recognizes are often background voices and lyrics more than the label-name soloists. Sundance-premièred 20 Feet from Stardom showcases those fantastic backing voices which come from largely unknown uncredited throats. Most names on the old vinyl covers near the ending only vaguely if at all ring a bell.

Last year’s This Time considered two individuals and one group -- the latter’s (the Sweet Inspirations) Cissy Houston is fleetingly in this 2013 documentary, too -- but with no viable connection among them, and with too many truncated clips, lacked focus.

This new Morgan Neville suffers from the rockumentary disease of trying to cover an abundance of riches that prevents any one from standing out in completeness. Its succession of clips and commentators grows thin, as the last of its ninety minutes drag and too blatantly hammer a point. But the singers are electrifying, at studio mics or in live concert footage.

It does not need the endorsements of Mick Jagger, Stevie Wonder, Springsteen, Sheryl Crow (once a backup herself) or Sting to tout the sounds of these (predominantly) ladies. Encomiums take up time better devoted to the subjects themselves, while the film descends to artsy bird-flock wheelings to Sting’s New Age-y whispers about soul and inspiration, artistry as opposed to money, luck or success.

Nobody here denigrates the white female singers shown surrounding, say, a Perry Como. “Competent” is the polite word used. But the roots of what is our contribution to music -- the “British invasion” was U.K. lads imitating the sounds of black America -- came from the call-and-response and choir of the black church, where many of the film’s singers got their start and to which some returned, like former Raelette Dr. Mable John.

The music business is famously cutthroat, unjust and rather amoral. Talent is not necessarily rewarded, nor lack of it a handicap; pluck and push still need a patron. Backups may not want the limelight and accompanying hazards -- “I wouldn’t be here talking to you; I’d be overdosed and dead” -- or may prefer inclusion in smooth group harmonies.

Or, courting individual fame, they may have trouble figuring why things misfired. Such is self-confessed diva Merry Clayton, though still humorous about a late-night 1969 call to sing with the Rolling Something-or-others, arriving with a big baby bump and hair-curlers, and blowing away the Brits on “Gimme Shelter.”

Or Darlene Love (née Wright), who, with L.A. session singers the Blossoms, did lead vocals on Crystal and Bob B. Soxx and the Blue Jeans hits but was not credited. Control freak Phil Spector “kept her in a box,” Motown had room for only one Diana Ross (though backup Martha Reeves and the Vandellas did push to the forefront), Atlantic would not tread on Aretha’s toes though there were other voices the equal of hers. When her contract was sold back to Spector’s Philles, Love left and wound up a housemaid but returned to vindication in her seventies -- “About time!” exclaims Bette Midler on introducing her induction into the Rock and Roll Hall of Fame in Cleveland.

Prodigiously gifted Claudia Lennear never wanted celebrity, though she did at one point shake a long leg as an Ikette; featured vocalist for The Color Purple, Puerto Rican Tata Vega had amazed Steven Spielberg by not being African-American.

A new crop of a Lisa Fisher or a Judith Hill has their choices to make, as well, especially since in twenty years technology obviates any absolute need for background singers or, with publicity, even for talent in frontliners. The pool of excellent singers has not shrunk, but conditions are changed. There was, and is, such talent that 20 Feet from Stardom, or any film, cannot hope to encompass it all, whatever niche is chosen.

(Released by RADiUS-TWC; not rated by MPAA.)