The first track on the new CD “Summertime: The 1963 St. Onge L.A. Duets & Narration” (AB Fable) is “Summertime,” and it has to be the most avant-garde version of George Gershwin’s most famous melody ever recorded. If I didn’t know who was playing, I would have guessed it was some combination of John Zorn, Stephen Bernstein, Olu Dara, and some other contemporary “downtown”- style players at home with free jazz and the great jazz standards. Actually, it’s the violinist Stuff Smith and the cornetist Rex Stewart, a pair of veteran players who were born in the first decade of the 20th century and who were already making vital contributions to the evolution of American music as early as the Jazz Age (and who both died in 1967).

Smith begins with a dramatic, classical-style intro on the violin before launching into a stately yet soulful reading of the Gershwin lullaby. Another instrument plays accompanying figures in the background, and it’s at least a whole chorus before we realize it’s a cornet stuffed with a tight plunger mute. In the second chorus, the cornet starts whinnying out a semblance of the melody via a variety of highly vocalized effects; now it’s the violin’s turn to play “second fiddle” and accompany the cornet’s lead, with mostly pizzicato plucks.

As the cornet proceeds, the instrument’s moaning and growling becomes more abstract, less directly related to the tune, while the violin gradually assumes its place beside it in the front line, playing all sorts of dark blues phrases. The cornet winds up by taking it down to a pedal note, out of the realm of instrumental and beyond human and animal noises into pure sound effects, something like a garbage disposal. By the coda, the two “voices,” violin and cornet, are gargling the tune in the most primitive, yet highly nuanced, way imaginable — it’s like Jackson Pollack meets Renoir in hi-fi.

This amazing five-minute reading of “Summertime” is merely the start of a fascinating, private recording of the two swing-era stars, made in 1963 by a jazz fan named Roger St. Onge at his house in Los Angeles. Mr. Onge’s plan was mostly to capture these two giants in a casual interview and off-thecuff performance. What he got was one of the most interesting documents of two jazz pioneers that’s ever been recorded, and it’s just been issued to the public for the first time as “The 1963 St. Onge L.A. Duets & Narration.”

Although the tape includes a lovely reading of Smith’s own “Take a Walk” (on which he sings and plays marvelously) and a spirited “Sunny Side of the Street,” the spoken portions constitute the meat of the matter. Stewart, best known for the 11 years he spent in Duke Ellington’s greatest band (and also for his brilliant work with Fletcher Henderson, Luis Russell, and in two outstanding sessions with Django Reinhardt), was the rare early jazzman with a profound sense of the historical importance of the music: He researched and wrote extensively, and at this gathering of St. Onge and several jazz-loving friends, he wanted to talk about what he lived and learned.

On St. Onge’s recording, Stewart speaks of Jelly Roll Morton and Bix Beiderbecke and how when he first came to New York from his native Philadelphia in the early 1920s his hero, the trumpeter Bubber Miley, brought him to Reverend Waller’s church in Harlem. There he heard, for the first time, the reverend’s son Thomas, a prodigious pianist then playing organ and not yet nicknamed Fats.

While Stewart can’t help lecturing (too bad he didn’t live into the era of jazz education), Smith can’t help living up to his reputation as one of the most flamboyant entertainers of the swing era. He continually undercuts Stewart’s speeches with little jabs from his violin, lapsing into the lachrymose “Hearts and Flowers” whenever he feels his friend is getting too serious. Smith finally quiets down when Stewart starts talking about him: The cornetist relates how he played through Buffalo with Henderson around 1927, where he met a lady pianist who bragged to him about her kid brother, who was playing incredible jazz on the violin. Stewart says he didn’t believe her, the violin just wasn’t a jazz instrument. But a few years later, Stuff showed up in Harlem and challenged the city’s reigning fiddle champ. “From that time on,” Stewart says, Stuff Smith “was recognized as the jazz violinist.”

This 1963 tape is being heard thanks to the efforts of Anthony Barnett, the world’s authority on the early history of the jazz violin. Mr. Barnett runs www.abar.net, which is a treasure trove of data on the beginnings of the hot fiddle, with particular emphasis on Smith and Eddie South (1904–62), who was the other great black groundbreaking jazz violinist. In addition to publishing his own books on the subject (he has done several full-length studies of both Smith and South) and producing his own CDs of the rare material he has collected, Mr. Barnett has worked on music projects by these two pioneers for Mosaic Records and, now for Jazz Oracle, a Toronto-based firm (www.jazzoracle.com). The latter company has just released an impressive three-CD boxed set of a series of prerecorded radio transcriptions by South, coincidentally also waxed in Los Angeles.

South, in addition to being perhaps the first important jazz violinist, was also one of the first black American jazzmen to be recognized in Europe, thanks in part to the Old-World nature of his instrument. Not long after an extended stay on the continent, South and his seven-piece band began working at the Club Ballyhoo in Hollywood, where they recorded a series of syndicated radio shows sponsored by a manufacturer of facial cream. The group, billed as “Eddie South and His International Orchestra,” offered a intriguing kaleidoscope of rhythms and melodies from all over the world — European waltzes, traditional songs from Germany and Hungary, the “goombay” rhythms of the Caribbean, what the announcer describes as “weird North African tribal melodies,” and “Ein spanischer Tango,” a Spanish tango written in Vienna and sung in German. It may not all be hot jazz, but it is all of extreme interest to jazz fans. Mr. Barnett has revealed to us a fascinating part of our collective heritage that we never even knew existed.

wfriedwald@nysun.com