The Goat Rodeo Sessions (Sony Masterworks, 2011)

In the pre-Beatles era, the term "longhair" was often applied to the world of classical music, and the title of this collaboration between a quartet of stellar string musicians from widely divergent genres suggests that legendary cellist Yo-Yo Ma and bassist Edgar Meyer - both among the premier classical musicians of their generation - are letting their hair down for a romp through the bluegrass world in which Stuart Duncan and Chris Thile are equally prominent.

A child prodigy on mandolin, Thile has carved out a progressive bluegrass notch through his work with Nickel Creek and the Punch Brothers for almost 20 years. Duncan continues to be the only fiddler in the long and renowned history of the Nashville Bluegrass Band and makes just about everybody's list as one of the top fiddlers in the genre.

As it turns out, though, the title hearkens from a common term for a situation in which a whole lot of improbable things have to fall into place before anything worthwhile happens, but when you play at the level these guys do, the improbable becomes commonplace. While there are distant hints of bluegrass and old time, the music here is solidly in Ma's and Meyer's ballpark.

There's a strong resemblance to chamber music, but Thile's mandolin adds a wild card to the mix, and on Where's My Bow? he shows he can match fiddle licks with Duncan. And despite the fact that, as the liner notes suggest, Duncan's music-reading skills are minimal, the impression here is that he could sit in with the Boston Pops and do just fine.

Though mostly instrumental, Crooked Still's Aoife O'Donovan adds an ethereal vocal touch on a pair of tracks, and she's particularly good with Thile on No One But You. It's not country by any standard definition, but "The Goat Rodeo Sessions" is exquisite music performed by four exquisitely talented gentlemen.