"We used to play in coffeehouses," says bluegrass musician Robin Williams. "You remember them, don't you?"

Ah, the coffeehouse. So many artists got their starts there. So few still exist. Luckily, the acoustic music that used to fill those smoky hangouts didn't disappear as well. Williams and his wife, Linda, mostly perform at festivals these days, such as the strawberry festival yesterday at Yosemite.

They began as a duo. Actually, they began dating. Then they started making music together.

"We met in a, well, a professional place," says Robin. "Okay, it was a bar. Linda was performing."

"I lived in Nashville," says Linda, "and when Robin was not on the road, he would come visit me and we'd play places in Nashville and work our duo material."

"Then we got married and decided to team up," he says. They both sing and play guitar, plus Linda plays banjo, "old-time clawhammer style," she says. And Robin plays harmonica. About two years ago, they added bassist and vocalist Jim Watson to the team. "We make a lot of music for only being three people," she says.

Over the years, the Williamses teamed up with a passel of talented folks: country music artists Chet Atkins, Don Williams, Leo Kottke, Doc Watson, Emmylou Harris and Hank Williams Jr., and yarn spinner Garrison Keillor, to name a few. The duo has been featured on Keillor's National Public Radio program "A Prairie Home Companion" as well as on his Second Annual Farewell Performance tour.

Robin and Linda Williams will be performing Thursday night at 7:30 at the Natural History Museum's Baird Auditorium. Tickets are $12 for Resident Associate Program members, $16 for nonmembers. For information, call 357-3030.