That's Show Business(1975)

Clement Mastard is the head of a leading journal dedicated to extravagant vaudeville. An unexpected contract requires him to reconnect with his former headliner Celia Bergson part to try to avant-garde theater. It is through this that he met Johann Sebastian Bloch, misunderstood musician who cause the loss but the side which Mastard, the man without scruples, to humanize and eventually produce a real masterpiece, the Missa Solemnis