Delta Sands is a place where lightly plucked cello can dance on the same plane as gentle rains of synthesizers. There’s a peace, not a tension, between these two schools of instruments. Both float together in Opal Onyx’s album-length dream, a deft and eerie debut grouped around singer Sarah Nowicki’s voice. Calling to mind the subdermal post-rock of both Thee Silver Mt. Zion and the Dirty Three, this Brooklyn-based electro-acoustic duo — Matthew Robinson completes the other half — deal in subtle, patient noir.