James DeVito pumps his fist and flexes a tattooed arm. Midway through an afternoon set on Day 2 of a three-day concert, his favorite band - read the tattoo - has just launched into "Buster," his favorite song.
The group, moe, had "teased" the tune the night before, plucking a few echoing notes before careering into another piece.
This time they run with it.
Crammed close to the stage at the Snow Ridge Ski Center and spread halfway up the deep-green slope, other fans, too, erupt in cheers, a familial feedback loop that seems to lift the smiling band.
Most in this camped-out crowd know the material well. Mr. DeVito, from Long Island, has seen moe 17 times in the past two years. Gary Scheller, a Grateful Dead disciple who has followed "jam bands" - groups known for their highly interactive, free-form live performances, the songs morphing into extended improvisational musings - since 1967, says he now sticks to shows closer to his home in Omaha, Neb. - except for moe or the Bonnaroo festival, the jam scene's annual "Woodstock" in Manchester, Tenn.
Ten years after the death of Jerry Garcia ended the long run of the Grateful Dead in its original form - and one year since the breakup of Phish, the Vermont band considered by many to be its spiritual successor - improvisational groups appear to be widening their collective fan base.
A relative granddaddy, moe was formed in Buffalo in 1991, the start of a rich decade for the genre. It has won both critical acclaim - Rolling Stone magazine gave its 2001 album, "Dither," four stars - and a fiercely loyal fan base typical of the offbeat genre's greats, among them Widespread Panic, The String Cheese Incident, and the more mainstream Dave Matthews Band.
Call it moe-mentum. This "moedown" over the Labor Day weekend - 16 bands on two stages - is now in its sixth year.
In a sign of the broader jam-scene's growth, Bonnaroo's producers have created Vegoose, a multivenue jam-band festival set to première next month in Las Vegas. "The whole jam-band vibe has definitely expanded," says Alan Miller, president of Filter Creative Group, which publishes Filter, an independent-music magazine in Los Angeles.
Among the reasons, say observers: fans' quest for community in the isolating age of iPod - and for unexpected and singular musical experiences in which they are active participants and not just the target demographic of rockers some see as increasingly corporate.
"The key to all of this is that [the band] is not just the 'supplier,' " says James Twitchell, a professor of English at the University of Florida, Gainesville, who writes about communities of interest and popular culture. "It's not as if some music impresario is twirling his mustache and saying, 'Let's trick these kids.' It's the 'consumers' who are essentially colluding, and generating this vibration."
For moe, the course of any given performance is a function of what's working at any given time, says Chuck Garvey, the band's lead guitarist. Its playlist is fluid. And the crowd shapes the show.
Random happenings do, too. At Turin last weekend, keyboardist Al Schnier brought his son, Benjamin, on stage for a brief planned appearance. When Ben left the stage, little sister Ayla walked on for some impromptu vocals, after which Mr. Schnier segued into "Chopsticks," as if to signal complete surrender to his toddlers' whims.
The concert, taped by scores of bootleggers (fan recording is openly accepted), was classic jam-band fare: A one-off combination of songs, snippets, and meandering riffs that draped a new aural tapestry over a thrilled live audience that ranged from young teens to graying boomers with children in tow.
"They might egg us on to push the outer walls of a song further and further," says Mr. Garvey of the crowd. "They'll say, 'Yeah, do it, we want you to do something new.' Well, we want to see something new, too.... More magic happens when you do things like that than when one person makes the decisions."
Innovation has kept moe in the limelight. In 2003, while touring its album "Wormwood," it was the first band to sell CD recordings of its concerts within minutes of the performances' end.
Like others in the scene, Garvey has some trouble defining jam-bands' art, something more than a fusion of influences.
"I think most of the bands have links to either the Grateful Dead or '60s psychedelic music in general," he says. "[But] you can have a rock-and-roll band, there are electronica bands and bluegrass bands that fall within the boundaries - anybody who has Americana roots, improvises, and is kind of eclectic."
Andy Gadiel, who runs JamBase.com, a San Francisco website, cites early improvisational jazz masters Miles Davis and John Coltrane as precursors to jam, and puts the Grateful Dead somewhere in the middle of the gnarled family tree. Like others, he calls the Dead's 1987 release "Touch of Grey" - a Top 40 hit - the trigger for a rush of more mainstream fans. Those fans were met with an institution.
"Deadheads from the '70s through the '90s - and by Deadheads I mean the legions of fans who began to follow the band through their big-arena show days - held a great spiritual connection between the music, the band, and themselves," says Pam Hunt, a graduate student in sociology at Kent State University who wrote her 2001 master's thesis on jam bands and has begun her doctoral dissertation on traveling communities.
Andrew Pearson, who came to Turin with Cortney Oliver on a side trip during a vacation in Burlington, Vt., all but abandoned the concert scene after following Phish between 1995 and 2000. Too many of his newer fellow travelers became focused on drugs, he says. They had no passion for the music, and served to advance a jam-music stigma: that it is just hazy background sound for hippie holdouts.
If that secret-society aura that attended the Grateful Dead has been diluted by the growth, says Mr. Gadiel, then maybe that growth will also open new doors to what he calls the "indescribable" phenomenon that tugs music fans to open fields to hear bands like moe, the Redwalls, and North Mississippi Allstars.
"Part of my crusade is to dissolve the stigma and make it less about the bands, less about any one type of fan," he says, "and more about good music."
Want to spread out on the grass and soak up hours of seamless jam-band music, whether it be blues, rock, or electronica? Pack a blanket, some water bottles - and be ready for anything.
"It's such a personalized experience that it's impossible to characterize," says Andy Gadiel, who runs JamBase.com, which tracks the improvisational genre.
Experiences can also be impossible to forget. Mr. Gadiel recalls a 1997 Phish show at which the audience collaborated on a 60-foot-tall structure, passing pieces of wood to the stage. After an encore, it was torched. "It was," says Gadiel, "quite a collective moment."
Other times it's just the pushing of musical boundaries - whatever the form.
"There are more than 30,000 bands in JamBase," he says. "So it's hard to pinpoint any one genre."
Here are a handful of jam-band festivals currently listed at JamBase.com:
The Big One
Athens County Fairgrounds
Artists include: Dave Matthews Tribute Band, The McGovern Brothers Bluegrass Band, and Grand Theft Audio Allstars.
Wormtown Music Festival
Camp Kee-wanee, Greenfield, Mass.
Artists include: Max Creek, Assembly of Dust, The Knot, and Zen Tricksters.
Austin City Limits Music Festival
Zilker Park, Austin, Texas
Artists include: Coldplay, The Allman Brothers, Lyle Lovett, and Government Mule.
Las Vegas, Nev.
Artists include: Dave Matthews & Friends, Widespread Panic, The Flaming Lips, Phil Lesh & Friends, and Trey Anastasio.