A Self-Critical Compositional Algorithm

A real-time system has been built which analyzes features of performed music and their evolution over time. Complementing this capacity are a set of compositional methods, which can generate or transform MIDI-level data. This paper describes a set of production rules, which have been implemented to allow the program itself to select compositional methods, and apply them, in real time. These production rules are expressed in the terms made possible by the analysis part of the program: the conditions evaluate logical expressions on feature classifications or descriptions of behavior. The execution part of the rules calls up composition methods to generate or modify material. The production rules implement a compositional critic, which is used to evaluate and modify the output of a real-time music system before the generated music is sent to the synthesizers. In other words, the critic forms the second pass of a system which generates material following some methods, then uses the critic to evaluate and correct the material emanating from the first pass. A discussion of the production rules and several musical examples are included.