Cold Mountain may be Tim Eriksen's first brush with the mainstream, but he's been making music for years. The Minneapolis-based singer, multi-instrumentalist, and musicologist lent his vocals to Brendan Gleeson's character and taught the rest of the cast, from Nicole Kidman to the Romanian extras, how to sing hymns in the Sacred Harp style--also known as shape-note singing because its hymnals use geometric shapes rather than conventional musical notation. Sacred Harp vocalists belt out the words with a lusty intensity that generates rough, clashing sonorities instead of the more familiar gospel harmonies. Eriksen has also played in hardcore punk and Balkan folk bands and studied Carnatic (southern Indian classical) music, and since 1990 he's pulled these genres together in varying combinations with the band Cordelia's Dad. His self-titled solo album, released two years ago by Appleseed Recordings, gives an idea of what this weekend's show will be like. Recorded live in the studio during one five-hour session, it showcases Eriksen's voice and occasional guitar, banjo, and fiddle accompaniment on a selection of traditional American hymns and folk tunes and originals that sound at home next to the older material. Eriksen will lead a two-hour shape-note-singing workshop Saturday afternoon at the Old Town School of Folk Music and open for Nina Nastasia that evening at the same venue. The next day he'll participate in the 20th annual Chicago Sacred Harp Singers Anniversary Singing at the Irish American Heritage Center--admission is free, but local singers are asked to bring a dish for a potluck lunch. Saturday, January 10, 2:30 (workshop) and 8 PM, Old Town School of Folk Music, 4454 N. Lincoln; 773-728-6000. Sunday, January 11, 10 AM to 4 PM, Irish American Heritage Center, 4626 N. Knox; 773-276-4277.