Abstract: A system and process for comprising a musical section in response to a user's interaction with a multimedia presentation is disclosed. The system includes a composition engine, performance engine, and arbitrator. The arbitrator provides an interface with an application program running a multimedia presentation. The arbitrator receives parameters from the application program indicative of a user's interaction and the type of music the application program requests in response to the interaction. The parameters are passed to the composition engine which composes a musical section having a chord progression and other data therein. The musical section and a style provided by the arbitrator are used by the performance engine to generate music sequence data for driving a musical instrument. The performance of the musical sequence data by the musical instrument occurs substantially contemporaneously with the user's interaction which caused the musical section composition.