Count this recording of a December 2002 North Carolina concert as one of the dividends of O Brother, Where Art Thou? Without that soundtrack's reach into the PBS audience -- the show is being broadcast on the network's "Great Performances" series, and there's a DVD with bonus tracks coming, too -- it's unlikely this collaboration would have come about. Its principals have performed in various pairings before, but it takes money and muscle to get these kinds of things on disc and until now, neither were much associated with bluegrass and its kin. With 23 tracks, the CD covers a lot of musical ground. Each of the principals does a couple of numbers with his own usual accompanists, Alison Krauss, to use the publicist's peculiar phrase, "drops by" to harmonize a bit, and there are some other enjoyable combinations of various personnel. Still, the central attraction is a set of eight numbers performed, with occasional bass accompaniment, by Earl, Doc and Ricky. Those are, if not earth-shaking, eminently worth the price of the set. Two come from the Flatt & Scruggs repertoire, a third from the album Watson cut with them in the early 1960s, two are genuine folk songs previously recorded by at least two of the trio, and all of those are performed with relaxed good humor and grace. The ultimate gems, though, are three numbers recorded by the Monroe Brothers in the late 1930s. On these, Scruggs is appropriately restrained -- there was no banjo on those records -- while Doc and Ricky channel the spirits of Charlie and Bill with spine-tingling precision. Skaggs, especially, perfectly captures Monroe's mandolin flourishes and the distinctive voice he used on those recordings. It's an absolutely riveting performance, and answers beyond all doubt any question as to why he got equal billing with the legends.