"There's no such thing as improvisation," the Grateful Dead's Jerry Garcia once said. "There's only composition. Only you do it quickly; you're composing on the spot."

This seems like a suspiciously semantic denial, but, if improvisational music does exist, what is it and what defines it? When a conductor interprets "St. Matthew Passion," what does that have in common with B.B. King playing whatever feels right over a 12-bar blues, or Ravi Shankar exploring the melodic possibilities of a raga, or John Coltrane working "My Favorite Things" until it explodes?

Clearly, the scope of improvisation in music is vast. Perhaps it is enough just to recognize that musicians have forever experimented with time and tone, crossing boundaries where it felt right to and, well, played with music as they play music.

This weekend, at Yomiuri Land's open-air stage, a full spectrum of expressive musicians will gather for the True People's Celebration, Japan's first large-scale outdoor event devoted to improvisational music. Among the acts performing will be Hermeto Pascoal, the Brazilian keyboard virtuoso who is also adept at playing, among other instruments, live pigs and his own beard; the legendary Sun Ra Arkestra, a group whose deceased leader, Sun Ra, was also known as the Philosopher King of Afro-Psychedelia; and several groups that represent the best of the ill-named "jam band" scene -- Medeski, Martin & Wood, The Slip and Black Frames (members of Critters Buggin). The roster will be rounded out with Japanese talent, including cutting-edge turntablists DJ Kazuma and DJ Klock, noise-trance practitioners Voordoms and even the bluesy, jazzy diva UA.

Beyond expectation

Improvisers can provide some of the most thrilling and challenging music on the planet, but they also have a reputation for sometimes emptying venues and horrifying even critics. Toward the end of his career, Coltrane's improvisations increasingly alienated his fans, who accused him of self-indulgence. John Zorn's experiments with duck calls and bowls of water in the early '80s were often met with hostility. And, of course, the good ol' Grateful Dead -- pioneers of very fast composition -- were long mocked as noodlers playing acid-trip soundtracks.

Speaking by telephone from Brooklyn, John Medeski, keyboardist of Medeski, Martin & Wood, commented on the risks involved in improvisation.

"[Improvisation] puts you out on a limb, and sometimes it probably sucks," he says. "But in the scene that we're talking about, everyone's willing to let there be some weak moments in order to get that thing that comes from true improvisation -- that cathartic, amazing religious experience."

Medeski concedes that not everyone is prepared for such sonic epiphanies. "It's language for another part of our existence, and I think people are way out of touch with it," he says. "You know, a lot of people don't want to really feel. They want to watch their little TVs and use their little air conditioners -- everything's within the realm of human control, as opposed to risking our lives or being awed or scared by something."

Saxophonist Marshall Allen, the current leader of the Sun Ra Arkestra, also noted how audiences have to develop inner tuning. Speaking from his home in Philadelphia, which he shares with several other band members, the 78-year-old Gemini says: "To some people, it sounds like a whole bunch of noise -- a lot of notes together -- that shocks and stimulates. If they can't find where they are supposed to be, but listen long enough, they will adjust themselves to the different sounds."

For the musician, however, Allen sees an even higher reward. "Improvising awakens the spirit, makes you feel good and heals your daily wounds," he says, nearly chanting the words. "You have to create -- that's your destiny. I try to circulate the air and make the music lift my feet, uplift me, up like an angel or something! Make me lighter! Lift me up and get all that heavy stuff off me -- defy gravity! I dream about it! I dreamed about being able to do that when I was young, and then I found myself on the other side of 50 and I'm dreaming about it still!"

Dreams come true

The True People's Celebration, which is expected to draw several thousand people, is the dream project of Phatleaf Productions, led by Taichi Komatsubara and Naito Hazuki. The duo met about a decade ago when they were both in college in Santa Monica, Calif., and Komatsubara swiped Hazuki's parking space in a crowded lot, making her late for a final exam. Despite their rocky start, they soon realized they were thinking on the same wavelength.

At their Ebisu office, they explain how Phatleaf was born in 1999 after Komatsubara quit his job as a booking agent and tour manager for a Japanese promoter who brought Grateful Dead cover bands to Japan.

"The Grateful Dead was a really great band that influenced people all over the world," Hazuki says. "But, at the same time . . ."

"The Long Strange Trip has been over . . . " Komatsubara picks up.

"Right," Hazuki says, "it was something in the past, it is not going on anymore, and we knew that there were other bands who were . . ."

"Alive."

Phatleaf built a solid following through its Organic Groove parties. Held at Tokyo clubs several times a year, these popular events combine foreign improvisational bands with sets from local DJs. And their success made both fans and organizers hungry for something more.

"The audience really wanted to see all these bands outdoors, and I really wanted to make more musical connections among the bands," explains Komatsubara. "These artists [at the True People's Celebration] are really connected."

Life support

It is one thing to have organizers with the vision to curate such a thoughtful lineup, but another for someone to come forward with the cash to back it.

In this case, that person was Takashi Kameda, chief executive officer of Tokyo Finance and Entertainment, Inc., which was founded last year.

Kameda knows it's not easy for lesser-known artists or promoters to find financing. "The banks only look for stable, nonrisky events. Venture-capital companies aren't interested in concerts," he says. "I want to create fun and pursue dreams and find people who have talent yet lack money."

The entrepreneur believes so strongly in this event that he has plunked down 30 million yen to help Phatleaf realize it. He says that as long as he sees some return on his money, he will continue to support the celebration. Indeed, Phatleaf is already planning an even bigger event next summer, most likely in Nagano Prefecture.

Medeski is extremely enthusiastic about the TPC, in part because of its uniqueness in Japan, but also because it is evidence that the global audience for improvised music is growing.

"When we first went out [to play live], there wasn't this support," he explains. "Now there's tons of bands out there, and they're all out playing music and getting by -- and they're not something created by MTV or a record company. They're doing it purely on the strength of their live performances."

If a definition of improvised music is impossible to arrive at, one fact is certain: The power of improvised music is best experienced live. Only onstage will you get the chance to see musicians like John Medeski and Marshall Allen unfurl their wings and take flight.