When this Canadian trio’s first album came out in 2001, it charmed the socks off listeners and critics, some of whom couldn’t quite figure out why. Warm, winsome, and delightfully frayed around the edges, Blue Horse is many wonderful things, but virtuoso is not one of them. Samantha Parton, Frazey Ford, and Trish Klein (and, on a few songs, Jolie Holland) harmonize gorgeously, but their voices are breathy and fragile, and while the acoustic arrangements are spot-on, the production clear and bright, no-one will confuse the relaxed musicianship on display with the “chops” approach that dominates so much of traditional and bluegrass music. Frankly, that’s a good thing. This is not folk for purists. Drums make more than a few appearances, 8 of the 12 songs are well-crafted originals, and even traditionals like “Rain and Snow” get an unexpected makeover, with mandolin and banjo plunking away to a reggae-inflected rhythm. But whatever its innovations, this is folk music in the spirit if not the letter of the Carter Family, situated firmly in the back-porch tradition of making music with friends and fellow travelers. On the best songs— “Light Enough to Travel,” a stunning version of “Lakes of Pontchartrain,” and especially, the infectious shuffle of “The Littlest Birds”—the joy of the musicians is palpable, and impossible to resist.