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What makes that song swing? Physicists unravel a jazz mystery / NPR

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NPR's Maria Godoy writes…Swing is an essential component of nearly all kinds of jazz music. Physicists think that subtle nuances in the timing of soloists are key to creating that propulsive swing feel. For nearly a century, jazz musicians and scholars have debated the answer to a musical mystery. As legendary jazz trumpeter Louis Armstrong once put it, "What is this thing called swing?"

Swing has long been considered an essential component of almost all types of jazz, from traditional to bepop to post-bop. As Ella Fitzgerald and many others have sung, "It don't mean a thing if it ain't got that swing." You might describe swing as a rhythmic phenomenon in jazz performances — a propulsive, groovy feeling that makes you want to move with the music.

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.

Ask a jazz musician what swing is, and you're likely to get the same answer Christian McBride gave me.

"Swing is a feel," says McBride, a multi-Grammy-winning jazz bassist, music educator and host of NPR's Jazz Night in America. "There's a certain language. There's a certain inflection of rhythm."

There's one defining component of swing that's easy to hear, and it has to do with how eighth notes are played. Instead of playing them straight, like this ...

McBride vocally demonstrates a straight eighth note

... in jazz these notes are swung, meaning the downbeats — or every other eighth note — is played just a little longer, while the offbeat notes in between are shortened, creating a galloping rhythm, like this.

McBride vocally demonstrates a swung eighth note

But jazz musicians know that technique alone can't explain swing — after all, even a computer can swing a note.

"A computer just ain't — excuse my language – it just ain't going to swing that hard, you know?" McBride says. "You still don't get the real proper swing feel, which is a human feel."

That swing feel happens as musicians interact in performance, McBride explains. "For me, I think you've got to lock people in and say, 'OK, here's where the time is, here's what the rhythm is.' And then everybody, collectively — the musicians and the listeners — can go, 'Oh, yeah ... that feels right.'"

But how exactly are musicians playing off each other to create that swing feel? That's what Theo Geisel wanted to find out.

The physics of swing - Geisel is a theoretical physicist with the Max Planck Institute for Dynamics and Self-Organization and the University of Göttingen in Germany. He spent decades studying the physics of synchronization — for example, how the billions of neurons in your brain coordinate with each other. He's also a passionate amateur saxophonist. He even has a band with other physicists. (They play at conferences.)

Geisel is now retired. That's given him more time to use his theoretical physics toolkit to explore other mysteries of the universe, including this one: How do musicians synchronize when they try to create swing in jazz?

"It's a general belief that musicians should synchronize as best they can when they play together. This is true, of course, to some extent," says Geisel.

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.        Bernd Thissen/picture alliance via Getty Image