The surge of interest in British folk music over the past decade has led to the resurrection of several careers, including those of fascinating artists like Vashti Bunyan and Bert Jansch. But the music never really went away, and few have so steadfastly carried the torch through the lean times as the superb family band Waterson: Carthy, members of which will be performing as a trio in this rare Chicago appearance. (Singer Norma Waterson, who’s been playing with members of her family in various combinations for more than 40 years, has unfortunately dropped off the bill.) Guitarist and singer Martin Carthy, perhaps best known as a member of Steeleye Span, has long trafficked in obscure, traditional songs, but he doesn’t get hung up on preserving every period detail. With daughter Eliza Carthy on fiddle and mandolin and Tim van Eyken on melodeon, the focus instead is on impressively lean arrangements and lovely vocal harmonies. a 7:30 PM, Old Town School of Folk Music, 4544 N. Lincoln, 773-728-6000 or 866-468-3401, $20, $16 kids and seniors. A