Jason Isbell came of age as part of the Drive-By Truckers' triumphant axis of songwriters, alongside Patterson Hood and Mike Cooley. Now that he's two years and two studio albums removed from the Truckers, Isbell remains every bit the embodiment of muscular, Southern-proud rock as his former mates. The Alabama native wears his roots on his flannel sleeves, evoking the sound of Alabama's Muscle Shoals Studio as well as alt-country rebels such as Slobberbone and Lucero. More rock than country, Isbell's latest album, Jason Isbell and the 400 Unit, is a versatile affair with slow-burning ballads and four-on-the-floor numbers that would make Tom Petty jealous. It sounds exactly like Isbell does live, thanks to a strong supporting cast and deliberate arrangements that never overplay their welcome.