For Pianist Michael Wollny, songs are like ghosts. His new album "Ghosts" is a gathering of some of the ghosts that regularly haunt him. Typically for Wollny, they range from classics like Franz Schubert's "Erlkönig" to jazz standards, film music, songs with a certain fragility by Nick Cave, say, or the band Timber Timbre, and also include his own darkly evocative original compositions.