Often enough, maybe too often, innovation in bluegrass amounts to softening of the sound with pop textures, chords and vocals. If the SteelDrivers are innovative, as they certainly are, they are not doing it by watering-down. What they're doing instead is giving bluegrass punch from other, more muscular directions. Those other directions are hard-core honkytonk -- not in itself all that surprising or original -- and also rock and soul. Now, that's new, particularly when you consider they're doing it within the genre's traditional acoustic stringband format. They're not, in other words, throwing electric guitar, piano and drums into the mix.

In fact, the integration of these genres into a bluegrass structure is so seamless that when I heard the opening cut ("Blue Side of the Mountain"), my initial thought was this was a neo-oldtime band, or at least a variant of the old Stanley Brothers mountain-bluegrass approach. Soon enough, I learned otherwise. Yet the SteelDrivers -- whose first album this is -- are traditional enough in their own way. The hard-core bluegrass audience, often resistant to the new (for reasons outlined above), has quickly embraced them, even if guitarist/lead singer Chris Stapleton's vocals seem influenced more by Stax than by Starday artists. Country music and soul music have been mentioned in the same sentences many times, but until the SteelDrivers came along recently, I doubt that soul and bluegrass have often shared even a paragraph.

The SteelDrivers consist of five Nashville professionals, studio musicians and in some cases songwriters, none heretofore associated with bluegrass. Some years ago, composer Mike Henderson (guitar, mandolin, vocals) released albums combining country, rock and blues well before such fusions were labeled alt.country/Americana. Tammy Rogers, who has played fiddle for various mainstream Nashville acts, is also a superior harmony singer. Richard Bailey plays full-strength, rhythmic banjo. Mike Fleming's stand-up bass could easily be dropped into a rock 'n' roll band.

Together, they fashion a fat, rich, tight approach powering the all-original songs into something that would never pass for casual background listening.

The songs themselves tend to the familiar themes of trad bluegrass -- passion, murder, prison, war, trains, alcohol, heartbreak -- of which no fan ever tires, since they're, of course, the natural language. Henderson and Stapleton write with such professionalism and assurance that a listener inclined to be critical may miss the naive (which is to say plain-spoken and sincere) emotionality of older bluegrass composition and performance.

Still, if 21st-century bluegrass is about taking what's usable from the past and finding a way to let it speak to a very different present, the SteelDrivers can only still fans' anxiety about the future.