After three albums as a member of Southern-rock unit Drive-By Truckers, Alabaman Jason Isbell struck out on his own with 2007’s Sirens of the Ditch. Jason Isbell and the 400 Unit finds Jason and his versatile backing band settling into a coherent and evocative groove, particularly on slow-burn numbers like the languorous “Sunstroke.” Most of the album resides somewhere in the territory of that dark-night-of-the-soul song, an atmosphere that practically demands the listener light up a cigarette and pour a glass of whiskey.