While anti-abstractionist and anti-structuralist in his approach, Ferrari creates music that is marked by a subtle poetic sense, by a love of humanity and its foibles, by humor, and an elegant, ephemeral sensibility.
His primary musical education was with Cortot, Honegger, and Messiaen (1946-1954) for whom he generated pieces in a free atonal style, such as the Antisonate for piano (1953) and the Piano Quartet (1954).
In 1958 he helped found the Groupe de Recherches Musicales (Group for Musical Research) and began the composition of his many electronic works, such as the Etude des accidents (1958), Tautologos I (1961), and Composé-Composite for orchestra and tape (1963). In the musique concrète piece Hétérozygote (1963 - 1964) that Ferrari refers to as "anecdotal music," there are fragments of conversations, and other sounds and noises from nature and daily life presented in an organized and poetic, although non-plot oriented manner. Bits of human speech in several languages are used both for their charm of meaning and their musical qualities of inflection and pitch — at one moment, several people are saying how much they enjoyed having visited some unnamed place, and at another moment a mysteriously transformed voice chants "dans un rêve" (in a dream) with accompanying like the creaks and crashes in a house during a wind storm; the result is not abstract but moves about the world with the ease of a thought or a dream. Ferrari also created one of the first works employing collective improvisation Spontanés in 1962.
Ferrari later taught composition in Cologne (1964 - 1966), and Montreal (1966 - 1969). His later works expand further upon his love of natural sounds and complex response to human behavior, including sensuality (for example, Presque rien avec filles/Almost nothing with girls, 1989). The Petite Symphonie Intuitive pour un paysage de printemps/Little Intuitive Symphony for a spring landscape (1973) is a lovely electroacoustic work that recreates experiences of the composer during a climb toward sunset on the Causse Méjean, a high plateau in the Massif Central "with sweet curves and gentle valleys...I wanted to accentuate this solitary and diffuse human presence by fragments of conversations which I had with some of the shepherds...one said: 'I am never bored. I listen to the landscape. Sometimes I blow into my flute and I listen to the echo which talks to me.'" The flute sound with multiple echoes returning from many surfaces continues in changing musical modes throughout the piece. For Brise-Glace (et si toute entiere maintenant...)/Icebreaker (supposing now I were to...) (1987), the composer combined electronically-transformed recordings made over a two-weeks sail aboard the icebreaker Frej with rich orchestral music and a text by Colette Fellous. A woman's voice delivers intimate, sensual impressions, as if in an interior monologue, while a passenger near the Arctic Circle: "The pilot comes very close to one's face to speak...I can still recognize the smell of him and the taste of his mouth, even though he is far away."