The Music of Erich Zann (1980)

Charles Dexter Ward, a young student of metaphysics, befriends Erich Zann, an elderly violinist who lives on the floor above him. Ward is fascinated by Zann's sinister yet wonderful music, which he hears late at night drifting down from above. But he discovers more then he bargains for when he peers at what beckons beyond that strange curtained window in Zann's room...