The Music of Erich Zann (S)

This story revolves around a student of metaphysics, Charles Dexter Ward who befriends Erich Zann an aging violinist who lives on the floor above him. Charles is fascinated and then drawn to Zann's sinister yet wonderful music that he hears late at night drifting down from above. He, of course, discovers more then he bargains for when he peers at what beckons beyond that strange curtained window in Zann's room.