From The Economist, December 6, 1997

Science and Technology, p. 92

Musical Computers

Miles Davis, version 2.1

Jazz conjures up images of dark, smoke-filled rooms and the strains of a saxophone or trumpet breaking away into a flight of fancy that often surprises the musicians themselves, not to mention the audience. While computers have long been able to reproduce synthesized music to command, they have not been able to improvise along with jazz's finest. Now, however, jazzmen have a digital rival.

John Biles, [an information technologist] at the Rochester Institute of Technology in New York state, has created GenJam, a jazz-playing computer that can trade fours and eights with the best of them. Originally developed four years ago, GenJam rapidly learned to improvise jazz with enough proficiency to fool a casual listener. But it has recently become a far better musician: it is now interactive, able to respond with its own musical whims to the music of its creator. And on December 4th, at the meeting of the Acoustical Society of America in San Diego, California, [Mr] Biles and GenJam were due to blow their trumpets.

When [Mr] Biles puffs away on his instrument, the sound is captured by a microphone that feeds into GenJam's "ear". This is actually a box known as a "pitch-tracker", which converts musical notes into their digital equivalents so that GenJam can perceive them. GenJam then picks another series of notes that sounds interesting and toots right back at [Mr] Biles through a synthesizer, even though it has never heard that particular piece of music before.

The secret of GenJam's prowess is the same as for all musicians: practice. Like any novice, it started off with some basic knowledge of the music it was about to play. A computer program told it the tempo and rhythmic style of the tune to improvise on, as well as the chord progression and the number of solos to perform. At first, it was also told in advance the drum, piano and bass sequence that it was to accompany.

To learn to improvise, GenJam relied on a computing technique known as a genetic algorithm. The algorithm starts out by generating a random set of notes that GenJam plays in accordance with what it knows about the piece of music. [Mr] Biles, as GenJam's mentor, listens to what it plays and translates his cheers and winces into language the computer can grasp by keying in a "g" (good for combinations he approves of, and a "b" (bad) for less pleasing sounds. This way, GenJam can assign a value to each section of the tune. In the next round, GenJam boots out the worst snatches of cacophony and replaces them with snatches that received the thumbs-up. It arranges these randomly to create a new set of melodies to play to [Mr] Biles, who then patiently puts GenJam through its paces once again.

Being a computer, GenJam has no ego and thus takes criticism well; and after several iterations of trial and error, it accumulates enough sequences of good notes to play something that sounds pleasing. This way, instead of just memorizing a particular melody, GenJam develops an aesthetic sense of what sounds good. When playing solos or replying to [Mr] Biles's trumpet, it draws upon this general training to jam away with what sounds like real soul.

[Mr] Biles has used this approach to train about a dozen different "soloists", each suited to playing a different style of jazz, from Latin to funk to new age. But like a real musician, even the same soloist sounds different every time it plays a tune.

[Mr] Biles says that playing jazz with GenJam is a lot of fun, but it can also be a bit unnerving. The computer's timing and technique are flawless, and it never plays a false note. Real jazz soloists bread the rules in interesting ways, which GenJam still cannot really do. However, imperfections in the equipment can compensate for this. For instance, the pitch-tracker may tell GenJam that [Mr] Biles has played an F sharp instead of an F -- but such small errors often add character to the performance instead of sounding like mistakes. GenJam's music is even good enough to satisfy jazz aficionados. Often the only reason that someone can tell that a computer is playing is because the synthesizer that produces the actual notes is not that good.

Although [Mr] Biles has played several gigs with GenJam under the billing of the Al Biles Virtual Quintet, he thinks that the visual impact of a live concert means that however good they get, computers will not put jazzmen out of work. Mr Davis's successors will raise their trumpets to that.

Note: [Mr] and [an information technologist] are corrections to the article as originally published.