This release on Denmark’s Dacapo label may seem an unlikely candidate for the classical best-seller lists, but several factors have propelled it to that level. Among these are the residence of the Danish String Quartet at New York’s Lincoln Center and the viral success of a video performance of some of a three-section wedding piece heard on the album. The quartet even raised funds for the release via a crowdfunding site, if not a first for the classical sphere then close to it. But the most important factor of all is that nobody has ever done anything quite like this before. The members of the quartet (in all but one case) have arranged folk songs of several Scandinavian countries for string quartet. That’s not a particularly common medium for folk song arrangements, but it’s the extremely varied nature of the arrangements that really stands out. The term “arrangement” isn’t even quite right; the 13 tracks take a step in the direction of classical compositions. The collection as a whole includes a large range of ideas, and so do many of the individual pieces, which gives the effect of examining the tune through a kaleidoscopic lens. A tune may be introduced by a slow prelude based on its collection of pitches, may be harmonized, made into polyphony, or subjected to deeper forms of alteration. It’s fascinating, it rewards repeated hearings, and it’s consistently lively and fun in a relaxed way. The sound, captured in a Danish museum hall, is superb. Possibly the sleeper classical hit of 2014.