The Nitty Gritty Dirt Band’s first new album in five years finds the group circling around to its earliest days as a rootsy rock band discovering country music. The covers here hail from the 1960s and ’70s (Stealer’s Wheel’s “Stuck in the Middle With You” and Canned Heat’s “Going Up the Country”), while the new “Jimmy Martin” pays tribute to the ornery bluegrass legend who appeared on their 1972 classic Will the Circle Be Unbroken. Nonetheless, Speed of Life has the feel of a push forward—a vital group assessing its legacy while continuing to add to it.