A whole album of bass and mandolin duets? It’s not only possible but bassist Edgar Meyer and mandolinist Chris Thile, two master musicians with roots in jazz, country, bluegrass, classical, and pop, have fashioned just such a disc. While this is a rather low-key affair, there’s still a lot going on--free-floating abstraction, rural mellowness, swinging jazz, pensive folk melodies, soulful classical motifs, and a few things that defy easy categorization. EDGAR MEYER & CHRIS THIEL is quiet, thoughtful music that’s both mellow and exhilarating.