We all know it when a piece of music swings, but have you ever asked yourself from where the groove comes? As it happens, musicians have long known that it’s all about the timing of notes, but it has taken until now for science to look into this in any detail.
Swing in music can be described as a feeling of being taken along by the beat rather than simply observing its progress. In jazz the effect the particularly marked, and the reason for this is that jazz musicians have a loose concept of time, allowing beats to be varied in seemingly arbitrary ways. Listen closely, however, and you’ll discover that there is nothing capricious in this deviation from the clock.
Physicist Theo Geisel and others have studied1 how the swing of jazz music is enhanced by delaying alternate notes within a bar by just 30 thousandths of a second. Above I talk of longer-scale deviation from regular metronomic beats, but it appears that the for want of a better term milligroove studied by Geisel and his colleagues is significant. From my perspective as a physicist and musician, this could account for the groove in non-jazz musical forms with a tighter rhythmical structure.
Looking at the Geisel study, when downbeats are delayed but offbeats kept the same, the music is more than seven times more likely to be rated by other jazz musicians as swinging, compared with music without delays. And there is no significant difference in music with delays in both downbeats and offbeats, when compared with the same piece of music with no delays at all.
The researchers show that short, systematic delays in the downbeats of jazz music significantly increases their swing rating, which suggests that delayed downbeats form a key component of musical groove.
Nelias et al., “Downbeat delays are a key component of swing in jazz”, Communications Physics 5, Article number: 237 (2022). doi:10.1038/s42005-022-00995-z