At this point, it's hard to believe that there's much unexplored territory in the musical spectrum for genre-busting guitarist Bill Frisell. But over the phone from a Calgary hotel room where he has just arrived, Frisell sounds almost nervous about his upcoming mini-tour of folk festivals.

"I've never done this before," he says hesitantly, though he finds encouragement in the globe-spanning range of music he has seen at the festivals thus far. "That's more like the way music is in my brain, anyway. Dividing it all up doesn't make much sense to me."

That restlessness is reflected in the constantly changing cast of musicians that accompany Frisell in his explorations. Just scrolling down the current tour dates on his Web site, the list changes from the folk fest string quartet through more traditional trio and quartet combos, on to the Unspeakable Orchestra, a conglomeration of improvisers from Frisell's electronica-inspired album Unspeakable.

And despite the presence of two working trios on his latest, the two-disc East/West (Nonesuch), Frisell just laughs when asked who constitutes his "regular" group. "I've been so lucky lately. There's this ever-growing circle of people that I've been playing with that know a lot of my music. So it's this luxurious situation where I can combine different people and see what happens."

By the time he reaches Philly, Frisell will have yet another new combo in tow, an organ trio featuring Sam Yahel and Joey Baron on drums. Frisell met Yahel, who has played extensively with saxophonist Joshua Redman, at a jam session hosted by drummer Brian Blade. The three played one tune and clicked so well that they later toured together.

"I wasn't looking for an organ player," Frisell explains. "It's more about Sam Yahel, the way his brain works. We just really connected in a good way."

Frisell's history with Baron stretches back much further. The two started playing together in the mid-'80s, with Baron playing in Frisell's first band as a leader. They later were both members of John Zorn's cut-and-paste thrash-jazz quintet, Naked City. For someone with Frisell's level of musical ADD, the extensive partnership is testament to Baron's own versatility and the shared chemistry.

Frisell describes Baron as "one of the closest friends I've ever had in my whole life, musically and in every other way. I'm really excited about this because we haven't played much in a long time."

Jazz organ, and the organ trio in particular, has experienced something of a resurgence lately. Traditionalists like Joey DeFrancesco attempt to fill the void left by the death of Jimmy Smith, while Medeski Martin and Wood take a more rock-influenced crossover path. Guitarist Skip Heller, who shares some of Frisell's roots-rock affinities, released two organ trio CDs earlier this year, paying homage to 1960s soul-jazz, to the extent of dropping Shirley Scott's name into a song title.

The tour with Yahel and Blade marked Frisell's first attempt at an organ trio, his only real prior experience with organ players being in high school funk bands. He stresses the "orchestral possibilities" of the guitar-organ combination. "It's like a string quartet, or a bluegrass band with a fiddle and a banjo and a guitar. There's certain combinations of instruments that just work together, and organ and guitar and drums work great.

"I like to play big, thick harmonic things. That's why 90 percent of the things I do, you're not going to see a keyboard player. I like to have all that space for myself. But there's something about the organ; there's a natural blend that happens. We can both be playing real thick harmonic things at the same time and somehow there's room for it."

Even with a catalog that takes in jazz, blues, folk, rock, metal and tributes to Walt Disney and Nino Rota, Frisell has never been one for faithfully replicating his sources. Instead, he voraciously assimilates everything he hears and uses it to guide his distinctively resonant guitar into new places. His take on the organ trio promises to be no different. "I'm not trying to play some retro funky thing. I'm still just playing whatever I would normally play."

Bill Frisell plays Sat., Aug. 13, 8 and 10 p.m., $30, Zanzibar Blue, 200 S. Broad St., 215-732-4500.

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Bill Frisell
East/West (Nonesuch)
Bill Frisell's latest live album devotes a disc apiece to two of his working trios, though with Kenny Wolleson the drummer on each, it is only the bass chair that changes. The Hal Willner-induced industrial experiments of his last CD, Unspeakable, have stuck with Frisell, as witnessed by the liberal use of tape loops and the manic traffic whirl of "Blues for Los Angeles." There is a high concentration of transformed pop tunes on both discs: "I Heard It Through the Grapevine" becomes a blues taken at a menacing lope, and "Crazy," a deep-bayou acoustic guitar duet between Frisell and bassist Tony Scherr.