A Generative Representation for the Evolution of Jazz Solos Kjell Bäckman*, Palle Dahlstedt IT University, Gothenburg, Sweden Abstract. This paper describes a system developed to create computer based jazz improvisation solos. The generation of the improvisation material uses interactive evolution, based on a dual genetic representation: a basic melody line representation, with energy constraints (“rubber band”) and a hierarchic structure of operators that processes the various parts of this basic melody. To be able to listen to and evaluate the result in a fair way, the computer generated solos have been imported into a musical environment to form a complete jazz composition. The focus of this paper is on the data representations developed for this specific type of music. This is the first published part of an ongoing research project in generative jazz, based on probabilistic and evolutionary strategies. 1 Introduction The most important feature of a good jazz musician is to be able to keep an entire solo together as an entity, i.e. to build up the solo phrase by phrase in collaboration with the other musicians, where each phrase is a natural continuation of the previous one and leads up to a climax of intensity. After the climax the solo should be rounded off. A longer solo might contain several climaxes, but they should then be organized in a musically meaningful way. A good improviser is not expected to drop the focus and give way to meaningless cascades of notes or producing routine phrases for lack of artistic ideas. The challenge is to be able to plan the structure of the solo already from start, and then stick to the plan during the entire solo. There are some excellent examples in the history of jazz with this ability, such as John Coltrane, Miles Davies, Keith Jarrett, Bill Evans, Claes Crona and possibly some more. This project aims at making the computer build up a solo based on these principles. This is done using evolutionary principles on a genome structure consisting of a raw melody line split up into small melody fragments (delta phrases) and a structure of operators applied hierarchically on the delta phrases. Initially, the raw melody line is built up according to a “rubber band” principle, where each pitch interval is constructed using energy constraints much like the tension of a stretched rubber band. After application of the operators, the delta phrases will be somewhat different, however hopefully preserving some kind of musical idea. The aim is to ensure logical development of a consistent material during the solo and thus reflect the feature of a well-planned solo. There are others working with similar concepts. Al Biles [1] has developed a system, GenJam, which uses phrases played by the “master” soloist as basis for the