Notes on Undulant

Abstract
This paper discusses how the author used a digital computer to compose his Undulant for seven instruments. In this process, the computer made compositional decisions at all levels of design: It first selected global attributes for each episode of the work (instrumentation; register, speed, length of phrases, and articulation for each instrument). It used this information to compose rhythms, including not only periods between attacks but also spacings and slurs. From the rhythms and how these rhythms correlated between simultaneous instruments, plus the registral information defined earlier, the computer deduced appropriate pitches. The pervasive technique thoughout this process was constrained search. Each search was recursive, so that whenever (as often happened) the computer attempted some decision where it deemed no choice acceptable, it could ÒbacktrackÓ, revise one or more earlier decisions, and try again. For each decision, the computer scheduled options Òon the flyÓ, making use of feedback from previous decisions.