Saint Louis Symphony Orchestra violinist Rebecca Boyer Hall comes prepared for the first question even before it is asked. "People often ask what the difference is between a violin and a fiddle," she says. "I've always liked Itzhak Perlman's reply: 'about $100,000.'"

Hall (whom everyone knows as "Becky") speaks with authority and experience about the differences between and likenesses shared in bluegrass and classical music. She began as a fiddler, growing up in a family of musicians that stretches back to her Irish-immigrant great-grandfather, a fiddler whose love of music passed through generations. Hall's parents are the former owners of that Webster Groves mecca, Music Folk. "I grew up in a family playing music and singing harmony before I had any formal training. I also grew up in a music store and learned to play everything that was hanging on the walls!"

With a childhood full of folk festivals and coffee houses and a family making music in the living room, Hall's membership in the Saint Louis Symphony Youth Orchestra brought a real problem: she couldn't keep her foot from tapping during a performance.

Hall, along with fellow SLSO musicians David Halen and Daniel Lee, will have no such worries when they perform with extraordinary bassist/composer Edgar Meyer and the stunning guitar/mandolin player Mike Marshall at the Afternoon of Bluegrass concert, the first of this season's SLSO Fusion Series concerts at the Touhill Performing Arts Center.

"I couldn't be more thrilled to be playing with Edgar Meyer and Mike Marshall," says Hall. "These are two guys who have been on top of their game for as long as I've been aware of great music."

"Great music" are the key words here. Neither Meyer nor Marshall fit into any single music genre. Meyer has recorded Bach cello suites on his double bass, composed a violin concerto for Hilary Hahn, and played his own compositions that hark back to the Scotch-Irish roots of bluegrass with such musicians as Yo-Yo Ma, Mark O'Connor, Joshua Bell, and Sam Harris. Another frequent collaborator, Marshall, has ventured into the musical realms of jazz, classical, Latin, and bluegrass. Even Afternoon of Bluegrass will be open to some genre bending.

Hall and her fellow SLSO string players wouldn't have it any other way. "I've been asked, 'Are you going to play fiddle music on that nice Italian violin?'" Hall says, rolling her eyes in amusement. "My answer is: 'I'm going to play all the great music I can on this nice Italian violin.'"

SLSO concertmaster David Halen grew up in fiddle country in Warrensburg, Missouri. "I was exposed to a lot of that kind of playing," he recalls. "It's part of our culture, and part of what orchestral musicians do when playing American music. You don't play Aaron Copland without playing some fiddle. My debut at Carnegie Hall as a soloist with the SLSO was playing electric country fiddle in William Bolcom's Songs of Innocence and Experience. I remember [former SLSO Music Director] Leonard Slatkin leaned over to me after that concert and said: 'We should take this back to Branson.'"

Halen has performed and taught during the summers at the Aspen Music Festival and School, which is where he got to know Meyer. "I know him socially from Aspen and I've played chamber music with is wife, [violinist] Connie Heard. Edgar does everything. He's one of the most amazing, gifted artists of our time. When he asked me if I'd take part in this concert last summer in Aspen — it's one of those opportunities you don't say 'no' to."

For Halen, the transition from classical to bluegrass has little to do with technique but more to do with approach. "It has to be free," Halen explains, "whereas classical music training tends to be so exacting because you're playing with so many different instruments — exactly as it is on the page. Bluegrass playing affords a lot more freedom."

Hall concurs. "In classical, the music is very learned. We are often working so hard at technical perfection; it's hard to let yourself relax into a different frame of mind, which is basically the difference: a frame of mind.

"Nothing is different technically," she continues. "I slightly relax everything — the bow hand might creep up — but it's about letting things relax a bit and letting in the inner self."

The crossover from one genre to the other is not so exceptional, as Hall observes: "When I began to study violin I most related to Bach, Handel, the Baroque composers, because they were probably closer to the folk music of their day. It's more improvisational. You hear this in Mozart, too."

Yet does Hall expect any difficulties when she crosses back to Mozart's "Jupiter" Symphony at Powell Hall (December 7-9) after playing bluegrass with Meyer and Marshall at the Touhill? Hall puts one foot over the other. "It will be like when I was in the Youth Orchestra and I had to keep my toe from tapping."

An Afternoon of Bluegrass, with Edgar Meyer, Mike Marshall, and musicians from the SLSO, will be performed at the Touhill Performing Arts Center on the campus of UM-St. Louis, Sunday, December 2 at 2 pm.

Eddie Silva is the publications manager of the Saint Louis Symphony Orchestra.