OmChroma (developed by Carlos Agon and Marco Stroppa) is a special-purpose library dedicated to the high-level musical control of synthesis processes. It implements the concept of a "virtual synthesizer" and currently calls the following real synthesizers : Csound (the most popular and widely used free synthesis software, available for different platforms ) and the Chant plugin of Diphone, developed at IRCAM by the Analysis and Synthesis Team and written by Adrien Lefèvre. OmChroma is a generalization of the kernel of Chroma (by Marco Stroppa), a system for the control of software synthesis he has been developing since 1980 first at the Centro di Sonologia Computazionale (CSC) of the University of Padova, then at IRCAM