New Orleans rowdies Dash Rip Rock have always had a split personality. Give them a juiced-up audience and they go for cheap thrills — they have to be the only band ever to play the Dogmatics’ aggressively un-PC "Pussywhipped" at their home town’s Jazz & Heritage Festival. But in the studio, they’ve never been quite sure whether to try capture the party-band vibe or bank on their songwriting.

Following a few changes of personnel and frontman Bill Davis’s move to Nashville (hence the shortened band name), Sonic Boom is the most polished and least Dash-sounding disc of their two-decade career. The Nashville influence is definitely there, in the harmonies, the fiddle, the steel guitar, and no fewer than three love ballads (bringing their overall total to, uh, three). Instead of making fun of Cajun music (they used to do a hardcore version of "Jambalaya"), they turn in a straight-up cover of the Crescent City standard "Opelousas Soustan."

Sounds like a recipe for sellout, but in fact this is the first Dash album that’s more than a toned-down version of their live show. Davis has made some big leaps as a songwriter, with a couple of tunes that would fit the old Dash format ("Plane Song" sends up their drummer’s fear of flying) and a bunch that wouldn’t. "High Speed Chase (on the Natchez Trace)" is a nifty cross between Skynyrd Southern rock and a Chuck Berry–style narrative; "Eventually Evangeline" sounds like an honest-to-God country hit. They almost trash the album’s grown-up feel by throwing on "Monkeys Comin’ out of Your Ass" (written by Jewel collaborator Steve Poltz, of all people). But old fans of this band will be happy to find it there.

(Dash join the Upper Crust this Friday, July 19, at 608. Call 617-591-1661.)