Robin and Linda Williams

Launched by A Prairie Home Companion just a few months after the program first aired in 1974, Robin and Linda Williams are to contemporary folk what Garrison Keillor is to Minnesota. Icons and avatars for acoustic music, the two have long dug deep into old-time traditions while writing their own material, honing their harmonies, learning to pick with bluegrass masters and dotting their humor with self-effacing squibs. If the musicians seem like sincere purists, it's because they are. But they're also smart and agile musicians who can rock the gospel and obliterate the heart — whether covering Hank Williams or singing seasonal tunes, as they will at the Sheldon this week.