Umphrey's McGee prides itself on being a band of thoroughly Midwestern boys from South Bend, Ind. But their eclectic mix of jazz, funk and prog-rock sounds too exotic for Indiana.

A sound like the skipping virtuosic groove Umphrey's employs normally belongs in L.A. or New York, not South Bend. But it's precisely this separation from time and place that sets the band apart. The boys from Indiana have managed to carve out a niche on the jam-band scene by defying all attempts at categorization.

They'll bring their unique sound to the high stage of the Orpheum Theatre this Saturday at 8 p.m. in a show co-sponsored by the Barrymore.

If past performance is any indication, the show will be long, loud and jam-packed in the improvisational sense. Over the past two years, Umphrey's has garnered a reputation as a group of mad virtuosos that can jam with the best. They're a band with something to prove, and they usually try to prove it by playing shows that can approach four to five hours in length.

It's an imposing proposition, even for fans of jam band music. But if you like a band that can groove but still challenge the ears with something new, Umphrey's fits the bill.

The band's website tells of "Umphreaks" and "McGeeks," fanatic followers who trade live recordings and form street teams to get the word out about upcoming shows. While it's doubtful that many fans actually use these terms, what can't be denied is that Umphrey's has been amassing a legion of fans over the past few years.

Unlike jam bands like the Big Wu and the String Cheese Incident, which draw heavily on traditional styles, Umphrey's strives to find new sounds. In the process, they've almost completely foregone the roots-rock influence of the granddaddy of the scene, the Grateful Dead.

Instead, Umphrey's jam sound is one part Frank Zappa, one part Rush and one part Phish. In fact, guitarist Brendan Bayliss' dry vocals sound eerily similar to Trey Anastasio's effortless speak-sing at times.

The obscure, intelligent lyrics are also reminiscent of the former Phish guitarist/vocalist. The verbose lines of many Umphrey's songs don't rival Dylan, but they fit the band's crisp, precise sound.

The band plays with prog-rock precision at all times, ripping through grooves like King Crimson. At the same time, they draw on several styles, most notably fusion-jazz and funk.

Many of their chords, rhythms and vocal melodies have a slightly dissonant jazz feel. These take getting used to, especially Bayliss' vocal lines, which sometimes jump in and out of tune.

But Umphrey's is equally partial to a low-down funk groove, especially in the middle of an improv section. Part of their skill as improvisers and songwriters is the frenetic ability to change styles and rhythms mid-song.

The latest release from the band, Anchor Drops, showcases this talent, with songs jumping from jazz to bluegrass to rock to honky-tonk piano with startling frequency.

Amidst all this talent, it's hard to resist the temptation to go overboard, and the band rarely takes the less-is-more approach. Everything, from the rhythms to the melodies, is complex and jaw-dropping, never simple. It can be a problem on some songs, as the combined might of the band just gets to be too much.

That's what turns off some straight-up rock fans. Unless you're into trying out what the band is selling, Saturday's concert will be a long four-plus hours.

Ultimately, however, it's hard not to be impressed by the band members' mastery of their instruments and tasteful touch. Umphrey's McGee is one of the most promising and unique bands on the jam band scene today, and they'll most likely prove it Saturday night for all those interested.