

Researchers at the University of Southern California have made a breakthrough in computer-generated music that involves generating harmonies in a number of specific styles for any melody. Similar work has been done along these lines but this is the first time the styles of various rock bands have been part of the equation.

Amateur musicians should eventually be able to use similar technology create entire songs using only a vocal melody and an idea of which band – or mix of bands – would sound right playing the accompaniment. Want a backing track for your "Somewhere Over the Rainbow" cover that sounds like a mix of Radiohead and Green Day? Soon, you could be able to click a button and make it so.

Pianist and professor Elaine Chew and Taiwanese rock guitarist and graduate student Ching-Hua Chuan (pictured to the right) have been working on "AutomaticStyle Specific Accompaniment" (ASSA) at the USC Viterbi School Department of Industrial and Systems Engineering for two years. So far, they have used the system on the music of Radiohead, Green Day and Keane.

This video compares the original accompaniment in Radiohead's "Creep" with a version automatically generated by ASSA. The system does not come up with every note laid down by Thom Yorke, Jonny Greenwood and the others, but 82 percent of the notes in a 54-note sample were precisely correct. More importantly, the computer-generated version comes close to the original in overall feel.

"We describe an automatic style specific accompaniment system thatmakessongwriting accessible to both experts and novices... the systemshould be able to identify the features important to the stylespecified by the user, [enabling the user to] ask for harmonizationsimilar to some particular songs," explained Chew and Chuan in a jointpaper submitted to the International Joint Workshop on ComputationalCreativity in London.

Even better, the system can learn how a specific band tends to dealwith harmony, so humans need not enter parameters to describe a specific band's harmonic tendencies. Instead, one must only feed songs by a given band into the system.

In the Radiohead example video linked above, for example, ASSA

listened to only three other Radiohead songs ("High and Dry," "Fake PlasticTrees" and "Airbag") before figuring out the harmonies for"Creep." Ostensibly, this system could be aimed at any song that hasbeen converted into MID, but eventually it could work on audio files aswell, given promising developments in automatic chord analysis.

Here's how ASSA works (image to the right). After ascertaining which chord sequences are possiblegiven a melody, the analysis portion of the system determines whichbranches were followed by a particular band on a chord-by-chord basis.

The second, generative part of the process then applies these choicesto the new melody to generate accompaniment consistent with the choicesthe band presumably would have made. It's a bit more complicated thanthat, also involving the insertion of checkpoints where the harmony iseasily understood by the system to anchor the generated chordsmore tightly to the melody, but that's about it.

If all you need is a melody, lyrics and a concept of which band orbands you want your accompaniment to resemble, the bar to songwritingwill be lowered. People are already recording much moremusic than they used to; if this system becomes polished, expect thenumber of new songs in circulation to increase even faster. Who knows, maybe bands will eventually be able to license their harmonic styles to other songwriters and performers.

Chuan and Chew plan to keep developing ASSA. One of their ideas involves "an end-to-end interactive prototype that will take userhumming input, create the accompaniment, and render it with theappropriate instruments."

Chuan claims that the processing demands of their system are not too steep and that the average PC should be able to run it.

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Images courtesy of USC Viterbi