Rock 'n' roll may have found a way to garner fans from the jazz audience: Do away with the instrumentation. That's what the Bobs, a Berkeley, Calif.-based a cappella quartet, did, and it will bring its act to Wolf Trap's Barns Saturday.

Two of the foursome, tenor/baritones Gunnar Madsen and Matthew Stull, had been with a singing telegram company and three years ago, says Madsen, "got the idea it would be fun to try a cappella versions of the Talking Heads' 'Psycho Killer,' and other weird songs." A classified ad turned up bass Richard Greene and tenor/alto Janie Scott.

Before they knew it they were getting jobs at San Francisco's Great American Music Hall and Los Angeles' Beverly Theater, were invited to perform at Scotland's Edinburgh Festival, had an album out on Kaleidoscope and got standing ovations on a jazz cruise that included saxophonist Stan Getz and vocalist Sarah Vaughan.

But the group's material is mostly originals in the style of contemporary rock -- songs with titles such as "Cowboy Lips" and "Art for Art's Sake," which "deals with what happens to your money in the hands of other people -- lawyers and gurus and drug dealers and that sort of thing."

"It's kind of relentless," says Madsen of the average rock group sound. "We're singing rock 'n' roll, but it's not going to have that heavy beat. When you sing it with four voices a cappella, it doesn't sound like rock 'n' roll anymore. What we do with our voices is try to imitate the sound of a full band and probably the chords we're using are just as complex as jazz arrangements. It's not jazz, it's not improvised, but it seems to really appeal to the jazz sensibility."