He studied composition at the San Pietro a Maiella Conservatory in Naples under the guidance of Achille Longo, his uncle.
[1] De Masi's filmography includes scores for over 200 films and TV series, ranging from Spaghetti Westerns and sword and sandal epics to gialli and horror films, such as Lucio Fulci's Lo squartatore di New York (The New York Ripper).
De Masi also scored several action films, such as Enzo G. Castellari's Quel maledetto treno blindato (The Inglorious Bastards), but he is best remembered for his work on Spaghetti Westerns.
Unlike most other composers, De Masi started writing western scores slightly earlier than the genre's most influential musician, Ennio Morricone.
In an interview, De Masi listed Palestrina, Karlheinz Stockhausen, Ravel and Shostakovich as his main classical influences.