Douglas McGray in Wired:
It all started more than 20 years ago. Cope, already an accomplished musician and programmer, sat at his piano, struggling to compose a piece. Desperate for inspiration, he imagined a computer program that could suggest a clever measure or two. So he compiled a database of his compositions and wrote some code that could detect patterns in his music and compose new riffs that follow the same rules. To his surprise, he says, the results "sounded like me."Since then, Cope has unleashed Emmy on dozens of the great composers.
Now it's Vivaldi's turn:
The audience hushes, and the ensemble begins: A single, piercing violin races through Vivaldi-esque arpeggios while the rest of the strings measure out a deep, deliberate complement. The second movement is different – slower, sadder, carried along by mournful viola. During moments of quiet beauty or apparent emotion, it is jarring to consider what the music means to Emmy – numbers, built on patterns, built on a database of more numbers. . . .After about 90 minutes, the performers take their bows to noisy applause. A small circle forms around Cope.
"Some of it sounded Vivaldi-ish," one woman admits, a bit grudgingly. An elderly woman calls it "wonderful."
I can't find samples of the Vivaldi, but this page includes excerpts of computer-generated pastiches of several other composers. None is thoroughly convincing, but they're all impressive, especially (in my opinion) the "Chopin."