Fado, Portugal's most famous musical style, has long been the object of a turf war between purists and those who would infuse it with outside influences. Singer Cristina Branco's in the second camp, and her latest album, last year's Ulisses (Decca), is her most radical manipulation yet of fado's essential sound--intense but elegant expressions of sadness interlaced with piquant guitar figures. The music is traditionally played on acoustic guitar, bass, and the trebly 12-string Portuguese guitar, but every song on the album features piano as well, and a few get viola and classical guitar. Guitarist Custodio Castelo, Branco's husband and longtime musical director, wrote many of the new songs, setting Portuguese poetry to original music. But the words for "Liberte" come from a poem by French surrealist poet Paul Eluard; Branco also delivers an English-language cover of Joni Mitchell's "A Case of You," and "Alfonsina y el Mara" dips into the graceful rhythmic shapes of Argentinean tango. In contrast to, say, fellow new-fado star Mariza, who employs a heightened dramatic formalism in her shows, gliding across the stage like a diva on wheels, Branco's a casual performer; at her last Chicago concert, in 2004, she wore jeans and cracked jokes. But nothing can lessen the impact of her exquisite voice--she brings a carefully controlled emotional depth and clarity to almost every piece. Sat 3/4, 7 and 10 PM, Old Town School of Folk Music, 4544 N. Lincoln, 773-728-6000 or 866-468-3401, $25, $21 seniors and kids. All ages.