The black string bands of the 1920s and '30s fused folk and blues roots with popular music, blazing the trail for bluegrass, western swing, and eventually rockabilly and rock and roll. Multi-instrumentalist Howard Armstrong is one of that era's few survivors. Armstrong began his career more than 65 years ago as a songster, playing folk, blues, spirituals, and pop tunes on fiddle and mandolin. A few years later, alongside bassist Carl Martin and guitarist Ted Bogan, he became renowned as a member of one of the most accomplished string bands. Today Armtrong is a veritable one-man folk festival, as famous for his handicrafts and paintings as his music. He's also known for his gentle dignity, which does much to dispel the stereotype of African American folk artists as quaint rustics. He'll be bringing along some of his handmade figurines for special pregig showings, and Louie Bluie, Terry Zwigoff's 1985 documentary about Armstrong, will be screened both nights as well (at 7 tonight and 8 Saturday). Don't miss this one: Armstrong is a national treasure, he's still near the top of his artistic powers, and even at his advanced age he has the audacity to keep growing. Tonight and Saturday, Rosa's, 3420 W. Armitage; 342-0452.