By Carl ZimmerMay 1, 1993 5:00 AM


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You are what you eat, and Eric Iverson’s artificial-life program eats Bach (or Gillespie, or Abdul). Then it spits out a new piece of music.

Ever since Pythagoras made numerical sense of octaves, fifths, and fourths, mathematicians have been stumbling onto hidden patterns in music. Over the centuries a few people have even tried to act on those discoveries and compose music mathematically. Nowadays that means using computers. One popular method is to generate notes randomly and then sort through them with an artificial-intelligence program--a set of general rules embodying the programmer’s vision of what makes music musical. Eric Iverson of New Mexico State University has an altogether different approach. He uses artificial life to tear an existing piece of music apart, digest it, and assemble the pieces into a new composition.

The term artificial life covers a wide range of computer programs that create simple automata, give them a few rules to follow about how they interact, and let them go about their business. In 1986 theoreticians at the Santa Fe Institute found that an artificial-life program could simulate a living metabolism, in which a few chemicals acting as enzymes digest other molecules and reassemble them into different ones in complicated cycles.

At the time, Iverson was a computer science graduate student at New Mexico State, with long-standing but uncoupled interests in artificial life and computer-generated music. When he read about the metabolism program, the proverbial light bulb went on in his head. If you think of the notes that make up a piece of music as a chain of chemicals, he realized, you could design an artificial-life program to metabolize it and create a new piece.

In 1990 Iverson went to the annual A-life conference at Santa Fe and told the experts about his idea. Though far from orthodox themselves, they thought he was crazy. He persevered, however, and the result is a music-metabolizing program called Metamuse.

When fed a piece of music--its usual meal is no more than a page long--Metamuse randomly extracts a string of four notes. That string serves as a digestive enzyme: it seeks out the same sequence of notes in the rest of the composition and cuts the composition in two in the middle of that sequence. The enzyme is rewarded by being allowed to reproduce itself, and the two copies then search for more matches. Whenever an enzyme reproduces, though, it has a small chance of mutating--of having one or more of its notes changed. Eventually, then, a bunch of different enzymes are at work, digesting and reproducing.

The digestive process stops when the entire composition has been reduced to a pool of fragments roughly the size of the enzymes themselves. Now Metamuse goes into reverse. The fragments reassemble themselves, each one looking for two other fragments to stitch together end-to-end. The sequence AABB, for instance, may link DFAA and BBDC into DFAABBDC. Once again a sequence that catalyzes a reaction is rewarded by being allowed to copy itself, and once again it is subject to mutation.

All in all, Metamuse is designed to preserve patterns in the music (by not cutting the fragments too small and by allowing the enzymes to copy themselves) while introducing novelty (by allowing for mutation and by stitching the fragments together in a different order). And since the program doesn’t contain rules about what makes music good, Iverson can let it eat any style he wants.

About a third of the time you get something you really like, and two-thirds of the time it goes off into the ozone, he says. I gave it some songs by Paula Abdul to get the ultimate pop song, but the best I got was something that sounded like a bad marching-band rehearsal. Given a snippet of a Bach prelude or a Dizzy Gillespie solo, however, Metamuse creates music that has structure and that preserves, at least to some extent, the spirit of the original--although the regurgitated Bach has twentieth-century angst.

Ultimately, Iverson would like to turn Metamuse into a composer’s idea-generating sidekick. Such software already exists in the artificial- intelligence format, but it is limited to a particular style of music. That type of program has a rigid, centralized control, says Iverson. This is a lot more fun to play around with. It will surprise you more.

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