Not one of the nine sister goddesses, Lady Luck must be kissing cousin of Polyhymnia, sweet-voiced Muse of sacred music and geometry, for this summer she gifts us with two superior music documentaries. Widely different circumstances separate the two, but they are united in celebrating the joys of soulful musicians without resorting to distracting gimmicks like underexposed swaying audiences and hey!-look-at-me backlit cinematography.

Remixed from the 16 mm stock that had miraculously survived, largely unprotected since July 1970, Bob Smeaton’s Festival Express records a surprisingly obscure train ride to venues across Canada. Though interspersed with well-done stage performances, it focuses more on its giants jamming, joking and schmoozing on the rented transportation. Hard to pin down to a single term, genres cross and combine in what is perhaps best characterized as roots country rock, with doses of Joplin’s blues, ‘fifties revival, even jazz riffs.

Slicker but no less wonderful is Antoine Fuqua’s Lightning in a Bottle with Martin Scorsese as executive producer. The former’s previous work with music videos and the latter’s experience in music documentaries, and both men’s love for the music and artists, serve them well, for they keep a no-profile and allow their subject to speak. Seaton’s feature début and Fuqua’s concert film share rare respect for their performers -- and have in common Buddy Guy and the Band’s Levon Helm -- in capturing them as people as well as musicians enjoying their craft.

Indeed lightning captured in a bottle, this second film is a record of the February 7, 2003, “once-in-a-lifetime ‘Salute To The Blues’ benefit concert” at Radio City Music Hall. The occasion was the centennial of “Father of the Blues” W.C. Handy’s first, fortuitous encounter with “the weirdest music I had ever heard,” a Tutwiler, Mississippi, black man’s sliding a knifeblade across guitar strings to sing about “where the Southern cross the Dog.”

The filmmakers wisely do not attempt the impossible, a definitive summation of the basic twelve-bar, repeated-lyric, speech-pattern rural song form and the basis of rock and even hip-hop and rap. Slaves’ African music combined with field hollers, church hymns, dance jump-ups, ballads, guitar call-and-response. Intercut with stills of slave auctions, lynchings, destitute African Americans, many of them actually projected as on-stage backdrop, and virtually opening with Angélique Kidjo’s “Zélie,” the film does not truly establish African roots per se, but, rather, African-American. Why quibble?

Recovered from a stroke, Ruth Brown mentions “life experiences” and male singers finding an acceptable outlet for tears; Shemekia Copeland finds the form “in my soul and in my spirit,” and, categorizing her and “Big Mama” Thornton, Dr. John speaks of male, rather than female, blues; Hubert Sumlin remarks that one doesn’t retire but “play[s] blues till you leave”; Bonnie Raitt emphasizes “juice and pain,” while archival footage has Son House’s “don’t be but one kind of blues. And that consists between male and female that’s in love.”

Mostly in concert but also in dressing rooms and in rehearsal at crosstown S.I.R. Studios, the talent is staggering, the list so long that the film must limit many to only a single number. Caught clear, sharp and no-nonsense, sometimes spotlight-bluish, hands and faces shine feeling and emotion, unobtrusive informative titles indicating song title and first performance. There are pleasant surprises, such as Natalie Cole’s sassy upbeat blues belting, and though emphasis is on performance, the brief historical footage and the off-stage banter prove unusually interesting. For instance, the mentor-pupil line running from Muddy Waters through Guy to Jimi Hendrix; “King” Solomon Burke’s reminiscences of performing for Klan-close Southern whites and of “Fats” Domino’s escaping through a window in which the even bulkier Burke got stuck; B.B. King’s Baltimore booing by rock ‘n’ roll kids and then crying onstage at the applause after his playing had conquered; the “neckbone circuit,” with its $14.27 pay, as opposed to the famous “chitlin’s” real $50; or that, unknown to Robert Cray until Copeland’s introduction of their duet, he had embraced her as a little girl.

The concert samples the blues’ different styles and, two-thirds in, a few minutes do flag when music that is good but really more white, blues-influenced countrified rock takes over; and the film entirely loses it during rapper Chuck D. and The Fine Arts Militia’s intrusive “Boom Boom,” Johnnie Lee Hooker’s 1962 sexy sweet-talking here re-worded to anti-war protest. A small flaw, a small price, as the performers themselves “weren’t getting paid,” in what should find its place among historic concert documentaries.

(Released by Sony Pictures Classics and rated "PG-13" for brief strong language.)