NPR posted a report on their web site yesterday called “What makes that song swing? At last, physicists unravel a jazz mystery.” It’s an interesting look at swing groove and how physicists who happen to be amateur musicians approached answering the question, what is swing?

Still, a precise definition of swing has long eluded musicians and scholars alike. As the Big Band era jazz trumpeter Cootie Williams once reportedly joked about swing, “Describe it? I’d rather tackle Einstein’s theory.”

Fittingly, physicists now think they’ve got an answer to the secret of swing — and it all has to do with subtle nuances in the timing of soloists.

What makes that song swing?

When I read that my first thought was, duh! Of course it’s soloist timing, and their relationship to the rhythm section groove. What could science actually say about this? It turns out the devised a pretty subtle experiment that helps answer the exact question of what a soloist does to swing hard.

But since the 1980s, some scientists and music scholars have claimed that the swing feel is actually created by tiny timing deviations between different musicians playing different types of instruments. To test this theory, Geisel and his colleagues took jazz recordings and used a computer to manipulate the timing of the soloist with respect to the rhythm section.

What makes that song swing?

They then played different versions of the recording with different timings to jazz musicians and asked them to rate the performances. By a large margin, the musicians preferred one set of timing over another, even though they couldn’t pinpoint what it was that was different. They then analyzed classic recordings by important and influential jazz musicians and discovered that they were manipulating their time in the same way.

What was that difference? Read the article or give the report a listen. Did you agree with the majority opinion on which manipulated recording sounded better? Can you notice the difference?