The ixi software project started in 2000 with the intention to explore new interactive patterns and virtual interfaces in computer music software. The aim of this paper is not to describe these programs, as they have been described elsewhere, but rather explicate the theoretical background that underlies the design of these screen-based instruments. After an analysis of the similarities and differences in the design of acoustic and screen-based instruments, the paper describes how the creation of an interface is essentially the creation of a semiotic system that affects and influences the musician and the composer. Finally the terminology of this semiotics is explained as an interaction model
