As Over the Rhine, the husband-and-wife duo of Linford Detweiler and Karin Bergquist have been sculpting their rich, atmospheric take on Americana for decades. The Long Surrender is a dark entry in their catalog, contrasting Bergquist’s milky, sonorous voice with shadowy mandolins and slide guitar on midnight waltzes like “Soon” and ghostly ballads such as “Days Like This.” Lucinda Williams guests on “Undamned,” contributing her velvety pipes to the duo’s dusky folk tapestry.