The Tri-Factor jazz trio - Billy Bang, violin, Kahil El'Zabar, percussion, and Hamiet Bluiett, baritone sax - has a very big weekend coming up.

They play at the Lincoln Center in New York City on Friday night, at An die Musik here in Baltimore on Saturday and at the HotHouse JazzFest Aftersets in Chicago on Sunday, in a celebration of 40 years of the Association for the Advancement of Creative Musicians. The Tri-Factor Trio is a kind of summit meeting of superb musicians. Various critics have named all three among the finest musicians in the country on their instruments. All three were finalists in the 2005 Jazz Journalist Association awards.

The Chicago-based El'Zabar says in a phone conversation that his colleagues are "two of the really special musicians in terms of their instruments."

They achieve a remarkable contrast, he says.

"One guy plays a really, really big instrument, Bluiett, but he has mastered and changed the nature of that instrument because of his control of the high register," El'Zabar says.

"And on the other end you got this little guy with this little bitty instrument that's always been associated with a more dainty kind of energy," he says. "But what he's been able to do with the violin is that he's made it as broad as any kind of saxophone."

El'Zabar, the nominal leader of the trio, joined the AACM in the early 1970s. The AACM is "a collective of musicians and composers dedicated to nurturing, performing and recording serious, original music ... Great Black Music." AACM has been an incubator of fine jazz musicians from trumpeter Lester Bowie to composer-saxophonist Anthony Braxton to, well, El'Zabar.

The Tri-Factor Trio's idiosyncratic, if not unique, instrumentation of violin, baritone saxophone and percussion has seemed a bit of an unusual innovation, even to jazz aficionados.

"But if somebody really studies jazz history," El'Zabar says, "[new instrumentation] has always been part of the experience and the experiment."

He tells people one of his main inspirations was Sonny Greer, the great drummer with the Duke Ellington orchestra.

"In the stuff of Duke from the '20s and '30s, you would hear kettle drums and bells and gongs and all kind of stuff in the arrangements," he says. El'Zabar adds African drums, thumb piano and chanting to the standard jazz drum kit.

Bang, in his turn, says he's played with El'Zabar at least 20 years. He says El'Zabar is not only an extraordinary percussionist, but an extraordinary person as well.

"And that always seems to work well," Bang says, by phone from his New York apartment. "When the person not only is a fantastic musician, but a good person, it seems to really round everything out. He's just a solid human being, straight-ahead, very sure of what he's doing. Very clear about things in life.

"As well as Bluiett. Because playing the music is [only] part of the day, after that we have to travel together, we have to live together, we have to talk together, we have to walk together. And that's just as important as playing on the bandstand. ...

"When days are as smooth as possible," he says, "you can put more into your art."

Bang has been busy all week, recording new work. His last two CDs - Aftermath and Reflections - were based on his experiences as a combat infantryman in Vietnam. And he flies back Monday from Chicago to play at a Labor Day Pray for Peace Concert sponsored by a Hiroshima organization in New York.

"I've performed in Hiroshima," Bang says. "That's where I actually met these people. I go to Japan a lot. They came to my concert there."

He agrees that the violin-percussion-baritone trio is "not a normal instrumentation."

"What makes that group work is not so much the instruments but the people involved," he says. "Everyone in the group is very strong on their instrument. We kind of blend together in a lot of ways to make it a sound of one."

He does make some adjustments. "Sometimes I hold down some ostinato lines that I wouldn't normally do because there would be a bass player doing that," Bang says.

Ostinato is a note pattern continuously repeated. The left hand in boogie-woogie piano plays ostinato.

El'Zabar also sometimes carries a rhythm line that a bass player might take and occasionally Bluiett does too, like the tuba player in a New Orleans jazz band.

Bluiett couldn't be interviewed this week, but Bang calls him "our chief." Chris Kelsey, in the All Music Guide, joins many other jazz writers in calling Bluiett "the most prominent baritone saxophonist of his generation," with a huge soaring sound that climbs from the horn's gut-bucket bottom far beyond its highest register into soprano sax territory.

"He's in charge," Bang says with a laugh. Bluiett has a reputation for prickly toughness. "Kahil runs the program but Bluiett is in charge."

Bluiett, who is approaching 65, is the respected elder of the group. He's a bit older than Bang at 58 and El'Zabar at 52.

"Bluiett's our sergeant at arms," El'Zabar says, fondly. "He really keeps us in focus. He's got some history. Bluiett is amazing. He really is amazing."

Everyone in the Tri-Factor Trio is.