Patty Loveless starts her show at The Birchmere, a music hall in Alexandria, Va., by performing contemporary hits like "I'm That Kind of Girl" and "Lonely Too Long" -- the kinds of songs that have made her a country radio staple. But midway through her set, Loveless and her musicians unplug and regroup. They cluster around a single microphone and break into the old-time, knee-slapping ditties from Loveless' most recent CD, "Mountain Soul", a celebration of the mountain music on which the Kentucky coal miner's daughter was raised. The audience jumps to its feet and begins to cheer and scream as if Loveless were doing magic tricks or acrobatics.

"I think we're onto something," Loveless says with a laugh.

She sure can say that again. Last year saw an almost unprecedented boom in all types of "roots" music. Everything from twangy bluegrass and mountain ballads to old-time gospel is suddenly back in style. "There isn't even another year we could compare it to," marvels Dan Hays, executive director of the Kentucky-based International Bluegrass Music Association.

Leading the charge was the startlingly successful soundtrack to the offbeat movie "O Brother, Where Art Thou?", a Depression-era retelling of the Greek epic "The Odyssey". The album has sold some 3 million copies, making it the best-selling soundtrack of 2001; it spent almost half the year at No. 1 on "Billboard"'s country albums chart. Even though "O Brother" was essentially ignored by country radio -- which favors safer, more pop-flavored fare -- it beat out offerings from heavyweights such as Tim McGraw to be named Album of the Year by the Country Music Association. Signature tune "I Am a Man of Constant Sorrow", a bluesy-twangy number that sounds like something the Waltons might have hummed along to, was the CMA's Single of the Year.

"O Brother" has even spawned a cottage industry. A Nashville concert by musicians who appear on the soundtrack inspired a second CD, a documentary film and the "Down From the Mountain" concert tour, currently selling out major cities. A whole new generation of fans is being turned on to the music of their grandparents' generation.

"Kids with nails driven through their noses come up to me and say, 'Man, that record rocks!' " says "O Brother" producer T Bone Burnett. In fact, one of the most buzzed-about groups on the scene is Nickel Creek, a Generation Y trio from San Diego whose sound defies easy categorization but whose roots are undeniably bluegrass. Fiddle player Sara Watkins, 20, describes her group's music as "bluegrass folk with some acoustic pop and a lot of instrumentals" (a cumbersome label she concedes "doesn't have that much of a ring to it").

Label or no, reviewers casually throw out words like "jaw-dropping" when talking about Nickel Creek. "Time" magazine named them one of its musical innovators for the new millennium. With virtually no support from country radio, their Grammy-nominated debut album has sold almost 400,000 copies in an industry in which a successful project might typically sell between 15,000 and 25,000 copies.

So what's going on here?

The prevailing wisdom is that consumers, tired of overproduced, cookie-cutter music created according to corporate marketing plans, are turning instead to the joys of music created solely for art's sake. Part of roots music's charm is that it can be a little rough and unpolished around the edges, including a healthy dose of improvisation.

"I think there's a groundswell for authenticity, away from this idea of perfect music," Burnett says.

The bluegrass association's Hays likens the newfound enthusiasm for roots music to what happens when you're accustomed to eating only fast-food french fries that have been "sliced and diced and fried and colored to a [specified] texture. Then all of a sudden you sit down in some funky little diner and they put real mashed potatoes with lumps in them on your plate. And you sit there and say, 'Wow! These are potatoes!' And in the case of something like Nickel Creek, it's mashed potatoes like you've never tasted before in your whole life," Hays says. "You want to kick yourself and say, 'Where have I been?' "