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The science of swing

With Ken Burns’s epic documentary Jazz airing on PBS, millions of people who never really gave much thought to this musical form before are suddenly learning all about its fascinating history—and more than once, they’ve heard that for music to be jazz, it’s got to swing.

Or, as Duke Ellington put it, “It don’t mean a thing if it ain’t got that swing.”

Up until now, though, swing has been one of those things that you either “got,” or you didn’t. There was no way to say, this swings and that doesn’t, except for a personal feeling.

No longer. As an article by Mick Hamer in the December 23 issue of New Scientist explains, swing has now been analyzed scientifically.

The basic rhythmic unit in jazz is the quarter note. That’s usually what defines the “beat,” what you tap your feet to. Melodies are superimposed over the beat, and are often made up of eighth notes, which, in classical music, are exactly one half as long as quarter notes. However, the jazz musician would play those notes alternately long and short, with the long note on the beat, and the short note off the beat.

That’s the basis of swing, but it’s more complicated than that. Making the long eighth note exactly twice as long as the short eighth note, like a drum machine, will make your “jazz” sound mechanical and dull—so Anders Friberg, a physicist at the Royal Institute of Technology in Stockholm, decided to see if he could analyze swing scientifically and see how real musicians play it.

He measured the ratio between the long and short notes of four drummers on a series of recordings, including Tony Williams, playing with Miles Davis, Jack DeJohnette, playing with the Keith Jarrett trio, and Jeff Watts, playing with Wynton Marsalis.

Friburg used a frequency analysis program to pick out the sound of the drummer’s ride cymbal from a series of 10-second samples. Modern jazz drummers usually play a pattern of quarter notes and eighth notes on this cymbal with their right hands.

Friburg found the ratio between the notes varied with the tempo. In slow pieces the long eighth notes were extremely long, and the short notes were clipped so short they were almost 16th notes. But at faster tempos the notes were practically even. Only at a medium-fast tempo of about 200 beats per minute did the drummers use the 2-to-1 ratio. (Of course, there were variations caused by the drummers’ styles and the group with whom they played, but the basic principle held true across the board.)

To further test his discovery, Friburg created a computer-generated version of a jazz trio playing the Yardbird Suite, by Charlie Parker. He played it back to a panel of 34 people at different tempos, and asked them to adjust the swing ratio. Sure enough, they preferred larger swing ratios at slow tempos and almost no swing at all at fast tempos.

The results explain why some musicians swing and some don’t. It takes split-second timing to hit the swing ratio just right. At a relatively slow tempo of 120 beats per minute, for instance, listeners prefer a swing ratio between 2.3 and 2.6—a pretty narrow window.

Friburg feels this relationship between swing ratio and tempo exists because there is a limit to how fast musicians can play a note—and the tempo at which listeners can distinguish individual notes. Too fast, and individual notes become “sheets of sound,” as tenor sax player John Coltrane’s first solo recordings in the 1950s were called by critics.

Friburg also looked at soloists, to see if they used the same swing ratios as drummers. He found that, while soloist’s swing ratios also drop as the tempo increases, drummers almost always use bigger swing rations—which is why the soloist can seem very laid back, even in a fast piece. He’s actually playing a little behind the drummer, so that notes that supposedly coincide with the beat may actually be as much as a tenth of a second late.

Friburg found that, instead of synchronizing with each other on the beat, as classical musicians do, jazz musicians unconsciously synchronize on the off-beats, the short eighth notes of the swing pattern.

There’s an old joke in which, coming into a club, someone asks the waiter, “How late does the band play?” To which the waiter replies, “About half a beat behind the drummer.”

Turns out that’s pretty much right—and that’s one reason the band swings.

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