SYSTEM OF A DOWNBEAT:

"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.

"We had experts -- professional and semi-professional jazz musicians -- rate how swinging these different versions of a tune were," he explains.

The song they manipulated was a recording of "Jordu," a jazz standard written by Duke Jordan. In one version, for example, the piano soloist started at the exact same time as the rhythm section. In another version, the soloist's downbeats started just the tiniest bit behind the rhythm section, but their offbeats were not delayed.

Even so, the jazz musicians who rated the clips picked up on it.

"They noticed a difference and they could feel the difference," Geisel says. "They told us that they could hear friction between the rhythm section and the soloist, but they were amazed that they could not identify what was going on exactly. "

Geisel says the expert musicians were nearly 7.5 times more likely to rate the version with the downbeat delays as having more of a satisfying swing feel.

In another part of the experiment, the researchers also analyzed a database with over 450 recordings of jazz soloists, including performances by the likes of Dizzy Gillespie, Joshua Redman and Charlie Parker. They found that almost all of them were using tiny downbeat delays relative to the rhythm section. "There were very few exceptions," Geisel says.

He says these tiny timing delays aren't random. They're systematic, though musicians are probably just doing it intuitively.

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