This paper describes recent enhancements in an interactive system designed to improvise with saxophonist John Butcher . In addition to musical parameters such as pitch and loudness, our system is able to analyze timbral characteristics of the saxophone tone in real-time, and use timbral information to guide the generation of response material. We capture each saxophone gesture on the fly, extract a set of gestural and timbral contours, and store them in a repository. Improvising agents can consult the repository when generating responses. The gestural or timbral progression of a saxophone phrase can be remapped or transformed; this enables a variety of response material that also references audible contours of the original saxophone gestures. A single simple framework is used to manage gestural and timbral information extracted from analysis, and for expressive control of virtual instruments in a free improvisation context.