Groovy jazz science shows downbeat delay is the king of swing

Swing in jazz music may rest on the placement of the downbeat according to research by scientists at the Max Planch Institute for Dynamics and Self-Organization in Germany.

We all know jazz has a certain “feel.” It’s often hard to describe, but it sets it apart from other genres of music. A large part of this is down to what is known as “swing” – probably the most iconic feature of jazz.

Jazz greats like Duke Ellington and Louis Armstrong were masters of swing. Benny Goodman was often referred to as the “King of Swing.”

While he definitely knew better than most, Louis Armstrong asks the question in his song: “What Is This Thing Called Swing?” Far be it from me (a classically-trained violinist and metalhead) to tell Louis how to play his notes, but I will indulge our readers in a Swing 101.

Swing is sometimes simply referred to as the playing of quavers (also called “eighth notes” because they represent one-eighth of a 4/4 bar) at uneven lengths, where other musical genres will have the quavers at the same length.

But the exact length of swung eighth notes has remained a mystery, even though jazz has been around for almost a century. Trying to quantify jazz’s most notable feature has proven difficult. Some even suggest that such endeavours perhaps take away from the genre’s charm. Jazz saxophonist Gerry Mulligan apparently said, “jazz is a music to be played and not to be intellectualised on.”

In his 1946 book, The Big Book of Swing, author Bill Treadwell argued “you can feel it but you just can’t explain it.”

But perhaps there is a science to swing after all.

This is what the Max Planck researchers sought to do. Their results are published in the Communications Physics journal.

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If we consider a 4/4 bar of eight quavers, “downbeats” are the odd-numbered quavers (the first, third, etc.) and “offbeats” are the even-numbered quavers.

The team analysed 456 jazz solos from various artists through the Weimar Jazz Database, which has an accurate record of details like note positions and rhythm. Isolating every downbeat-offbeat pair, the researchers looked at the average swing ratio (length of each note in the pair) and delay of each note in the solos using the downbeats of the drums as reference.

They found most musicians, regardless of subgenre, preferentially delayed the downbeats by a tiny amount. This delay becomes smaller as the song’s overall tempo is increased.

For an intermediate tempo of around 150 beats per minute, the researchers found that downbeats were delayed by about 9% of a quarter note length.

“Of course, the magnitude of downbeat delays may vary within a solo or a whole piece and it makes sense to also look at individual delays in their musical context,” the authors write. “Here, however, we want to detect general trends and are therefore studying average quantities.”

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The researchers also looked at the ratio of length between downbeats and offbeats.

Though classically trained, my musical education did include some lessons on swinging. We were taught, as a guide, to think of swung pairs of quavers as having a “triplet feel” meaning that the downbeat is twice the length of the offbeat.

The authors’ results demonstrate “that the noted triplet feel (or ternary feel, i.e., a swing ratio of 2:1) is rather a myth as far as soloists are concerned. Most of them use swing ratios that are below 1.5.”

To further study swing, the Max Planck scientists manipulated a soloist’s section from three songs: “The Smudge,” “Texas Blues,” and “Jordu.”

In one set of manipulated recordings, the downbeats were delayed by 30 milliseconds. In another, both the downbeats and the offbeats were delayed.

The researchers played the audio to 19 semi-professional and 18 professional jazz musicians to give their rating of the level of swinging they heard. The musicians were asked “Did it swing?” and “Did it groove?” Answers were given on a scale of 1 (“not at all”) to 4 (“very much”).

The musicians gave the highest swing ratings to versions of the songs with delayed downbeats and undelayed offbeats. The musicians were 7.48 times more likely to say the song was swung with delayed downbeats.

No discernible difference in swing-level was found in versions with both downbeats and offbeats delayed compared to the originals.

In comments to the online study, some of the musicians indicated they couldn’t perceive the small 30 millisecond delays in the downbeats. “They apparently could ‘feel it,’ but they just couldn’t ‘explain it,’” the authors write.

“These small downbeat delays were not perceivable as such by professional jazz musicians in the recordings. The much larger delays in laid-back playing – on the other hand – are easily perceivable and are also applied to offbeats, even though the detailed nature of delays in laid-back playing still remains to be clarified in future work.”

As groove is closely related to swing, the results are unsurprisingly similar in the groove ratings.

Interestingly, the professional musicians gave overall lower ratings than the semi-professionals. A more discerning ear? A bit of pomp? Maybe they’re just such cool cats that they have high expectations.

Conducting a similar analysis of latin music, the researchers found downbeat delays, where they occurred, were very small and sometimes negative. It seems that downbeat delays are a particular feature of swinging jazz.

“Our findings are of interest to various fields, from the physics of social interactions and human behaviour to psychoacoustics and the perception of musical rhythms,” the authors write. “They also have implications for music education and music production.”

Now that’s pretty fly.

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