Gregory Alan Isakov, “Appaloosa Bones” (Dualtone/Suitcase Town Music) Gregory Alan Isakov surfaces on old playlists as the artist most likely to send you looking to remind yourself who that is — so sweetly and gently understated that it's sometimes easy to forget the source. On “Appaloosa Bones,” Isakov's first new album in five years, he only adds to the mystical aura he created in his earlier work, including the Grammy-nominated 2018 album “Evening Machines.” His new songs are relentlessly majestic, a kind of musical morphine, invariably soothing. There's enough beauty in them to work as background music but enough substance to reward listeners who lean in more actively.