FAME Studios founder Rick Hall, left, worked brought Clarence Carter and musicians of all stripes and sounds to record in the tiny Alabama town of Muscle Shoals. (Magnolia Pictures)

What is it about Muscle Shoals that has made it such a mecca for musicians? That this small Alabama town on the banks of the Tennessee River has been able to produce and sustain not just one world-class recording studio, but two — FAME Studios and Muscle Shoals Sound Studios, both of which have drawn flocks of musicians of every stripe — is surely due to some kind of mojo.

The word “magic” is mentioned a lot in “Muscle Shoals,” a mesmerizing documentary that tries to explain, or at least place in context, the extraordinary success of FAME (founded by producer Rick Hall in the late 1950s) and Muscle Shoals Sound (a competing studio spun off in 1969 by members of FAME’s original house band, known as the Swampers). It’s as good a word as any to capture the ineffable quality of the Muscle Shoals sound, which is a blend of hillbilly music, blues and spirituals, among other diverse influences.

“Queen of Soul” Aretha Franklin, one of many musicians featured in the film who recorded in Muscle Shoals, calls that sound, in a nice turn of phrase, “greasy.” Reggae star Jimmy Cliff, who also recorded there, believes there’s a field of mysterious energy in the town. But it’s rocker Bono who speaks most poetically of the place’s mysterious sonic power, saying it’s like “the music comes out of the mud.”

What the U2 frontman is doing in the film isn’t exactly clear. Bono isn’t identified as having ever recorded in Muscle Shoals, although he comes across, somewhat grandiloquently, as the resident expert.

However it is characterized, the Muscle Shoals sound is clearly more a function of Rick Hall’s ear — and drive — and the Swampers’ musicianship than anything else. The film emphasizes one incongruous fact: Hall and the Swampers are white, while such black singers as Arthur Alexander, Percy Sledge and Wilson Pickett were responsible for many of FAME’s earliest hits.

One interviewee relates a particularly telling anecdote. Paul Simon, who recorded several tracks on “There Goes Rhymin’ Simon” (1973) at Muscle Shoals Sound, called songwriter and Stax Records producer Al Bell, asking him, “Hey, man, I want those same black players that played on ‘I’ll Take You There.’ ” Bell, who wrote the 1972 Staple Singers hit, replied, “That can happen, except these guys are mighty pale.”

This colorblind recording history is fascinating. Several people in the film reminisce about how pioneering Hall was in his championing of black musicians, in both a place and a time in which segregation was still the norm.

The list of musicians appearing in “Muscle Shoals” who speak of their studio experiences there is long, including Gregg Allman, Etta James, Alicia Keys, Keith Richards and John Paul White of the Civil Wars. The diversity of the group, whose music runs the gamut from Southern rock to blues, speaks to the hard-to-pigeonhole nature of the sound that has come out of Muscle Shoals and that continues to make an outsize dent on our grateful eardrums.

★ ★ ★ ½

PG. At West End Cinema. Contains some obscenity and drug references. 111 minutes.