DOCUMENTARIES have shed light on the studio musicians who flavored Hitsville U.S.A. smashes ("Standing in the Shadows of Motown") and the muddy Southern soul/swamp rock that rose out of "Muscle Shoals."

The 2014 Academy Award-winner "20 Feet from Stardom" focused on backing vocalists, mostly females, who made the stars sound lots better.

There's a somewhat different twist, though, to the finally sprung tale of "The Wrecking Crew," the 20-some musicians who ruled the L.A. recording scene in the latter half of the 1960s and early '70s.

In that emerging era of self-contained singing/playing bands (a trend/necessity brought on by the Beatles and Rolling Stones), musical guns-for-hire like guitarists Tommy Tedesco, Al Casey and Glen Campbell; bassists Carole Kaye and Joe Osborn; keyboardists Don Randi and Leon Russell; sax man Plas Johnson; and drummers Earl Palmer and Hal Blaine weren't just hiding behind the curtains.

They were helping to commit fraud.

As far as the public and even some of the "industry" knew, the guys shown on the record covers, making the TV appearances and working the concert tours who called themselves the Association or the Beach Boys were the same lads doing all the playing on the singles and albums.

But if you could worm your way through the back door into the recording studios, as Tedesco's filmmaker son, Denny, does here, you'd find a not-so-handsome but far-more-talented bunch of musicians toiling away. Versatile talents who would ride the surf one hour for Jan & Dean, build a Phil Spector "Wall of Sound" as the Ike and Tina Turner Band (on "River Deep Mountain High") the next, then shift gears and shake their Mexicali jazz tail feathers a couple of hours later as the Tijuana Brass. (And in their spare time, lay down memorable riffs for a gazillion movie and TV themes.

Even "American Bandstand" mover/shaker Dick Clark didn't have a clue that "certain people didn't play their own records, until the Monkees came along."

"Come on, we were actors playing a TV band," dismisses Monkee man Micky Dolenz, with a laugh. (Quite likely he's the rebel who first spilled the beans, admitting that the emperor was not wearing clothes.)

For the Beach Boys, having studio musicians toil away on "Good Vibrations" with mad genius front man Brian Wilson, while the rest of the troupe toured, was a logistical solution to "coordinate our schedules," rationalizes the group's Al Jardine. And saved the already feuding band from tearing each other apart.

How good was the Wrecking Crew, as they were informally known? In a "Guitar Player" interview a few years back, Philly-based jazz master Jimmy Bruno said that ring leader Tommy Tedesco (who died of lung cancer in 1997) was an "absolutely amazing" sight reader. "He could be talking to you while he was doing it."

In the film, singer/guitarist Roger McGuinn, of the Byrds, admits that Crew cats needed only a couple of takes to make "Mr. Tambourine Man" a hit. But when the "real" Byrds insisted on cutting the follow-up tune themselves, "Turn! Turn! Turn!" took 78 takes (stretched over five days) to perfect.

For this music fan, getting to meet odd-girl-in Carole Kaye is the doc's extra-special treat. Bass in hands, she demos how spur of the moment riffs she (and the other "guys") invented could turn a dishwater dull tune like "The Beat Goes On" into pure gold.

Such rescue missions should have won 'em a writing credit and royalties (as "beat" makers earn today), but then was just part of the job.