This feels like a warm welcome back from two old friends you haven’t seen in a long time. Fourteen years after Raising Sand, Robert Plant and Alison Krauss have reunited. “Can’t Let Go” — written by Randy Weeks and originally recorded by Lucinda Williams — is the first single from Raise the Roof (out Nov. 19); the collaborative album produced once again by T-Bone Burnett. The duo’s mellifluous harmonies return, filled with the longing (or pleading) of two lovers who face the inevitability of lost love, anchored by the shuffling grooves of drummer Jay Bellerose. It seems like time hasn’t passed at all.