In this article the authors discuss real-time musical applications using the IRCAM (Institut de Recherche et de Coordination Acoustique/Musique) Signal Processing Workstation: this is an intuitive and straightforward user interface, intended for use by musicians. They present techniques for filtering, cross-synthesis, noise reduction, and dynamic spectral shaping, along with control structures that allow for both fine timbral modification and control of complex sound transformations using few parameters.