Algorithmic composition is the technique of using algorithms to create music.

Algorithms (or, at the very least, formal sets of rules) have been used to compose music for centuries; the procedures used to plot voice-leading in Western counterpoint, for example, can often be reduced to algorithmic determinacy. The term is usually reserved, however, for the use of formal procedures to make music without human intervention, either through the introduction of chance procedures or the use of computers. A (largely academic) distinction is sometimes made between composers who use indeterminate (e.g. stochastic) procedures to compose music and those who use routines which produce deterministic results given a fixed input into the algorithm.

Many algorithms that have no immediate musical relevance are used by composers as creative inspiration for their music. Algorithms such as fractals, L_systems, statistical models, and even arbitrary data (e.g. census figures, GIS coordinates, or magnetic field measurements) are fair game for musical interpretation. The success or failure of these procedures as sources of "good" music largely depends on the mapping system employed by the composer to translate the non-musical information into a musical data stream.

Composers known for their use of algorithmic procedures:

• John Cage
• Iannis Xenakis
• Charles Dodge
• Paul Lansky
• Karlheinz Essl

Algorithmic techniques have also been employed in a number of systems intended for direct musical performance, with many using algorithmic techniques to generate infinitely-variable improvisations on a predetermined theme. An early example was Lucasfilm Games' 1982 computer game Ballblazer, where the computer improvised on a basic jazz theme composed by the game's musical director. A more advanced implementation of this is present in the music subsystem of Microsoft's Xbox games console - the game plays variations on a human composer's theme, but varies its improvisations based on real-time events in the game (so, for example, the music sounds more staccato and dramatic during fight scenes, but is gentler and more mellow afterward).

Similar generative music systems have caught the attention of noted composers. Brian Eno has produced a number of works for the Sseyo Koan fractal music system, which produces ambient variations for web-pages, mobile devices, and for standalone performance. The copyright status of these "generative" works is unclear: Sseyo claims to own the copyright of all final Koan performances, although the original "composition" is supplied by the composer and the "performance" is largely the result of the user's computer's own random number generator.

Samples of algorithmic music

• A sample of Ballblazer music: OGG vorbis format, MP3 format (details)

External link

• Sseyo homepage (http://www.sseyo.com/) _ including generative music plugin and links to composition tools
• Realtime Composition Tools (http://www.essl.at/software.html) _ generative computer programs for composition, live performance and sound design by Karlheinz Essl