Folk has become, for some, a four-letter word. Rusby’s sweet, melancholic voice, and her way with harrowing old ballads, could change that. Rusby’s already well established, with four albums and fans like Bonnie Raitt and Richard Thompson. But she deserves a much wider audience. It may come with her latest, which displays her knack for making ancient heartbreakers like “Cruel” and “Sweet William’s Ghost” sound as relevant as any indie-rock hit. Her own songs, like the gentle “Falling,” are pretty damn fine too.