Meaningful real-time interaction between human performers and computer processing is an important aesthetic issue for many composers. With the advent of computer systems that are actually fast enough to permit real-time algorithmic sound realizations based on the analysis of live performance data the issue now facing composers is how to utilize these tools in a meaningful and artistic way. Lyra, composed in 2002 for violin and Kyma, is an environment in which the acoustically generated sounds and the computer generated and processed sounds are mutually dependent upon each other for a unified ensemble performance. All of the computer music layers are generated in real time using the violin music as direct audio and as analyzed input data for processing, resynthesis, and other parameter control. The violin music is also affected by the computer music output through performance instructions that invite response and improvisation. The violinist is also able to control macro time and gestural synchronization with the computer sound layers. The aesthetic goal is to create a performance environment that permits maximum flexibility for the human performer with a great deal of linear independence for both violin and computer, while still maintaining a very high degree of unity and ensemble interaction.