Mandolinist David Grisman is best known for the fusion of bluegrass, jazz, and Grateful Dead-style jamming he’s christened “dawg music.” But in Retrograss, his trio with folk icons John Hartford and Mike Seeger, he applies old-fashioned bluegrass instrumentation to rock and R & B numbers–an idea that came to him when, years ago, he heard a European group tackle bebop and post-Coltrane free jazz with a Dixieland lineup. Seeger, whose instruments include guitar, Autoharp, banjo, and fiddle, has dedicated his life to preserving the traditional music of the American south; Hartford picks banjo in the sparse, rhythmically square pre-bluegrass mountain style, and his fiddling shows the influence of everything from Celtic ballads to Appalachian breakdowns. The band’s only album so far, the 1999 Retrograss (Acoustic Disc), is an inconsistent, fascinating mess: the old-timey treatment doesn’t flatter Otis Redding’s “(Sittin’ on) The Dock of the Bay” quite the way it does the Beatles’ goofy “When I’m Sixty-Four.” Hartford’s mannered vocals are the disc’s most serious flaw, especially on Chuck Berry’s “Memphis” and the Redding tune–he often sounds like he’d rather be somewhere else. And on “Hound Dawg,” a sparse arrangement of the Big Mama Thornton song Elvis made famous, Hartford and Grisman’s stilted enunciation comes off as almost parodic. Bob Dylan’s “Maggie’s Farm,” on the other hand, works fine as a Dock Boggs tune, and Berry’s “Maybellene” sounds appropriately hot-blooded propelled by the boing-boing of Seeger’s mouth harp and Hartford’s bluesy banjo–probably because Berry adapted it from a country song in the first place. Unsurprisingly, Retrograss does just as well, if not better, when it covers folk and bluegrass tunes: Randall Hylton’s “Room at the Top of the Stairs” prickles with existential dread, Hartford’s fiddle bawling convulsively over Seeger’s obsessive single-chord banjo patterns, and standards like Earl Scruggs’s “Flint Hill Special” and Jimmy Martin’s “My Walking Shoes” practically catch fire. It’s hard to predict what will happen at these concerts–on disc, the chemistry between these three staunch individualists is uneasy at best–but they’re all so talented that anything they do is worth a listen. Sunday, October 22, 4 and 7 PM, Old Town School of Folk Music, 4544 N. Lincoln; 773-728-6000.