At a secure 73, Willie Nelson’s not about to change to please a hot young alt-country buck, his taut touring band, or the sizeable audience of hipsters they might bring along with them. So though he says in the press release for Songbird that Ryan Adams “was really the main guy here,” this latest entry in the old-icon-meets-young-iconoclast trend is lit up by the sparks between the principals (“We came from extremely different places, and we didn’t always agree”). Willie and his long-time harmonica player Mickey Raphael roll along their melancholy, jazzy way, unperturbed by Adams and his band as they rock with guitars and keyboards that alternately chime and churn. After the straightforward blues opener, the contrast mostly enlivens these two originals (one by Adams, one by Nelson) and nine covers (including three originals from Nelson’s back catalogue) in offhand and off-kilter ways. The title track rushes by in two-thirds the time it took Christine McVie to warble it with Fleetwood Mac, yet the words stick the way they never did on Rumours. And “Amazing Grace” is reborn in the saddest version of a joyous standard I’ve heard since Nelson cut “Blue Skies” back in 1978.