Artificial Music: The Evolution of Musical Strata

The Abstracts section ofLeonardo Music Journal is intended to be a rapid publication forum. Texts can be up to 750 words in length with no illustrations, or up to 500 words in length with one black-and-white illustration. Abstracts are acceptedfor publication upon recommendation ofanyone member ofthe Leonardo MusicJournal Editorial Board, who will then forward them to the Main Editorial Office with his or her endorsement. ARTIFICIAL MUSIC: THE EVOLUTION OF MUSICAL STRATA Andrew Horner, Andrew Assad and Norman Packard, Center for Complex Systems Research and CERL Sound Group, University of Illinois, Urbana, IL 61801, U.S.A. Received 15 October 1992. Accepted for publication Uy RogerF. Malina. As the most abstract of art forms, music is often regarded as a human re-creation of nature. This idea is supported by the fact that development within a musical composition is clearly some sort of evolutionary process. In this respect , music may be considered among the earliest of artificial systems. We are thus led to suggest that music be used as a model for exploring and quantifying evolution. Some of our previous work has utilized evolutionary processes in musical composition [1]. That work entailed the use of genetic algorithms to thematically bridge sections of music. The composer specified the initial and final themes, the duration of the bridge, and a collection of developmental operators . The genetic algorithm then had to find a sequence of these operators that could transform the initial theme into the final theme within the timeframe specified by the composer.© 19941SAST ABSTRACT Our current work allocates more of the creative compositional tasks to the computer, including the allocation and scheduling of musical lines. The fitness of any given line is highly dependent on other lines near it temporally and textually; thus, successful music entails the evolution of groups of individual lines that interact in musically meaningful ways. When musical lines work together as a group they form a strata. Generally, members of a strata are perceived as a unit within the texture as a whole. In our work the dimensions of pitch and stereo location provide a space in which melodic metrics can be defined and strata can develop. The concept of musical strata is analogous to that of a colony [2]. Like individuals within a musical strata can engage in competition and cooperation . In a colony, members compete in an ecological space, while in a musical strata they contend within a musical space. Similarly, as individuals can increase a colony's overall average fitness by cooperating to improve resource distribution within the colony, musical lines within the same strata can complement one another to improve the "fitness " of the strata. Our preliminary work has implemented the above ideas. Within our environment , two initial lines are randomly generated. These individual musical lines consist of thematic patterns in pitch and amplitude domains encoded in a chromosome-like structure . The thematic material does not manifest itself entirely until the individual fully matures, so individual characteristics are gradually uncovered as time progresses. When an offspring of an individual is reproduced, it receives the parent's thematic material with possible mutations. Within the environment, individuals desire to increase their energy level, which directly controls their overall amplitude , thus bringing energetic lines to the listener's attention. This competitive jostling is highly characteristic of real musical performers. The principal method of increasing one's energy level is to try to join or create a compatible strata. When lines enter a strata, they agree to "stick together" for some period of time, and they will move as a whole over that duration. Benefits are paid to members of a working strata in terms of increased energy levels. However , these benefits must be divided among the individuals of the group. This discourages the formation of giant monolithic masses. Moreover, the division of benefits among the lines is not equal, but proportional to their current energy levels. Since individuals are allowed to leave a strata periodically, they can seek their fortunes elsewhere if unhappy or, alternatively, a strata can dissolve only to reform minus despotic or parasitic members. The lifetime of a strata is limited even when benefits are balanced among individuals. The benefits paid...