As Buell E. Cobb Jr. pointed out in The Sacred Harp: A Tradition and Its Music, whether or not Sacred Harp singing is in fact folk music is the subject of some controversy. Aside from practitioners’ shunning of the label, arguing against such a designation is the fact that the music is distributed in book form, the 1991 edition of The Sacred Harp shape-note hymnal (not to be confused with Cobb’s study) having inherited a corporate legacy that stretches back to Benjamin Franklin White’s 1844 edition. Although Sacred Harp singing has a strong geographic base in both New England (where the surprisingly effective shape-note system was devised to encourage the participation of novice sight-readers) and the South (where country churches took up the practice with fervor), it is wholeheartedly evangelical, devotees often traveling hundreds of miles to welcome neophytes to such gatherings as this weekend’s Potomac River Sacred Harp Singing Convention, then devoting part of the proceedings to their instruction. The evidence for the a cappella form’s folk status, though, is strong enough to convince Cobb, and I’m inclined to agree. At the heart of Sacred Harp practice is a democratic tradition that must be spread via participation, not performance. You’d never believe from its appearance on the page how wild this stuff is. In catering to the untrained voice, the Sacred Harp unleashes the free, full-throated harmonies of what Alan Lomax called “a choral style ready made for a nation of individualists.” From 7:30-9:30 p.m. Friday & 10 a.m.-5:30 p.m. Saturday at Pohick Church, 9301 Richmond Highway, Lorton.; and 9:30-3 p.m. Sunday at the National Cathedral School’s Hearst Hall, 3612 Woodley Rd. NW. FREE. (202) 546-2228. (Glenn Dixon)