Just what the hell is “folk music?” Is it the hollers and spirituals of African-American slaves? The 19th-century minstrelsy of Dan Emmet? Is it the blues Howlin’ Wolf brought out of the cotton fields, the torment Hank Williams carried into the beer joints? Or is it the reedy, sanitized shtick of Pete Seeger, the tremulous, lite-operatic warble of Joan Baez? Ever since the 1950s “folk revival” began, the new idiom steadily reduced its musical sources to a bourgeois-palatable dilution, becoming a style defined not so much by the authenticity and power its originators displayed, but one that had to be presented with timid, obsequious deference—as if trading in the down-at-the-bottom reality that spawned the songs would sully forever the button-down shirts and cardigan sweaters of its well-fed university audience. At this late date, with all that happily behind us, it comes down to the music itself, and Marley’s Ghost, a drastically talented old-time string band, puts it all into some sharply-focused, much-needed perspective. The quintet works their esoteric repertoire with swinging authority and a dog-eared rock & roll heart, and have nailed all the power, purity and weight of a wildly freewheeling, archaic set list. As featured on their current Van Dyke Parks-produced Spooked CD, it encompasses Civil War era ballads, songs of the sea and soul-stirring gospel, and Marley’s Ghost hits it with a mix of intricate harmonies, instrumental prowess and a cheery bite that combine for tremendous effect. Best of all, unlike their revivalist forebears, there’s nothing phony about it.