In this brief article, the author explains the compositional principles of his work Préfixes (1991) for instrumental ensemble and MIDI clavier. The composition represents a new “mixity” between direct sound and loudspeaker sound that has come out of computer synthesis. Préfixes is the logical outcome of the author's development of the principle of hybridised sound. Hybridisation affects the transients of attack: the neuralgic and decisive moment from which instrumental sound surges. The theory of mixity concentrates on the hybridisation that results from fixing signalling particles to the initiative of a sonorous, acoustic entity.