Like many singer-songwriters, Jason Isbell writes music that mirrors developments in his own life. In recent years, that’s thankfully included the hard-won contentment he’s experienced on his path to 40: sobriety, marriage and on from there. On this summer’s The Nashville Sound, the decorated Alabama-born star understandably casts his gaze toward parenthood — a job he’s recently come to share with singer, fiddler and Tiny Desk veteran Amanda Shires — but expands his scope further to encompass politics, fear of obsolescence, and his place in the world. It’s a gorgeous record: noble and scruffy, graceful and human.