By Jon Garelick

Welcome back! The second half-life of the Either/Orchestra.

Either/Orchestra at Regattabar — a welcome return for a jazz band that remains a refreshing outlier in form and content. Photo: Paul Robicheau

It was no surprise that in the second set of the Either/Orchestra’s first performance in six years, the band sounded a little rusty in places — a bit of tentativeness, perhaps, and maybe some intonation problems here and there. Bandleader Russ Gershon (Arts Fuse interview) jokingly characterized the first set as occasioning “a few train wrecks” and a “high body count.”

Nonetheless, this show — December 17, the 40^th anniversary to the day of their debut at the Cambridge Public Library, in 1985 — was a welcome return for a jazz band that remains a refreshing outlier in form and content.

Russ Gershon of Either/Orchestra at Regattabar. Photo: Paul Robicheau

It’s hard to overstate the extent to which the Either/Orchestra broke the mold for jazz bands in 1985 — this at a time when the David Murray Octet was a going concern, as were the Henry Threadgill Sextett and hard-charging Steve Lacy bands. The E/O’s brought their own sense of irony and theater to the jazz scene — from their first LP, Dial “E” (with its cover photo of cinema icon Sergei Eisenstein making the call) to pranks like proclaiming one of their performances “Bill Walton Night” (an event at which the Celtic great made a surprise appearance).

But such gimmickry belied serious musical intent (my first piece about the band, in The Boston Phoenix, was headlined “Serious Monkey Business”). Gershon and others of the band’s arrangers loved unlikely mash-ups of genres and eras. At a show decades ago, he introduced one tune as “a cross between ‘Africa Brass’ and the theme from Mannix.” But it was no joke. Or, it wasn’t only a joke. Gershon’s “Benny Moten’s Weird Nightmare” (“Moten Swing” taken in Mingus-like directions) sealed the deal, earning a Grammy nomination for the arrangement. The band eventually delved into Afro-Cuban music (Afro-Cubism, 2002) and, perhaps most famously, Ethiopian jazz, recording for the esteemed éthiopiques series and performing locally with Ethio-jazz stars like the composer Mulatu Astake.

In two completely different sets at the Regattabar, the band played across the entire discography, with a chunk of the first given to their “Ethiopian Suite.” The second set (the one I attended) opened with one of their classic mash-ups, a funked up version of Thelonious Monk’s “Nutty” joined to Bobbie Gentry’s “Ode to Billie Joe,” the latter introduced by Gershon’s plaintive statement of the theme on tenor (in an arrangement by former E/O keyboardist Kenny Freundlich). The finale was “Red,” Robert Fripp’s composition for King Crimson, with an arrangement by former E/O guitarist John Dirac (and the original drummer from the album track, Jerome Deupree, sitting in at the R-bar).

Vincente Lebron of EitherOrchestra at Regattabar. Photo: Paul Robicheau

So it was no surprise that the latter — a mammoth arrangement with multiple tempo and rhythmic shifts — didn’t quite come into focus, despite the guitar-god efforts of guest J. Johnson. The “Nutty/Billie Joe” opener likewise had its shaky moments (despite a pointed piano solo by Alexei Tsiganov) as did the swinger “H.A.C.”

But things picked up with “Amara Rumba” (from the band’s second album in the éthiopiques series), with bassist Rick McLaughlin, percussionist Vicente Lebron, and drummer Brooke Sofferman locking into the groove under the snaky melody. Here the musical and emotional high point of the night came from Either/Orchestra founding member Tom Halter, now living with Parkinson’s Disease, who played a trumpet solo from the audience front row, seated in a wheelchair. Halter (who is a specialist in mariachi music) gave full force to his opening notes, broad and smeary, and then quickly began nailing phrases with precise rhythmic fire, shaping them into a long, arcing climax.

Joel Yennior and Charlie Kohlhase of Either/Orchestra at Regattabar. Photo: Paul Robicheau

There were other appealing details throughout the night — new bandmember Sam Spear’s “middle-eastern” minor-mode clarinet obbligato under the closing chorus of “Amara Rumba,” Charlie Kohlhase’s fearless altissimo alto sax cry at the end of the Ellingtonian “The Half-Life of Desire,” and the Ethio-jazz “Kèsét Eswa Betcha,” with a measured call-and-response between brass and reeds over the 6/8 groove, an extended percussion duo for Lebron and Sofferman, and a floor-rumbling low-note blast from trombones and, I’d guess, Kohlhase’s baritone. And then there were the arrangements themselves: always with contrasting dynamic and timbral effects and a continual unfolding narrative of shifting themes.

It was a long night — the first, sold-out, show, scheduled for 7:30, started late and ran long. The second set, scheduled for 9:30, started at 10:19 and ended at 11:35. But it was good to see the Either/Orchestra packing them in again. Gershon announced that coming shows include Cleveland, New York, and the Big Ears confab in Knoxville. And maybe, he said, there will even be some new tunes. Can’t wait to hear them.

Jon Garelick, a former arts editor at The Boston Phoenix and Opinion page staff member at The Boston Globe, can be reached at garelickjon@gmail.com.