You can feel swing, but you can’t explain it – many jazz lovers were convinced of that. A research team has nevertheless dared to try and actually found an explanation as to which musical aspects convey the jazz-typical swing feeling to the listener. Using computer manipulated jazz pieces evaluated by professional musicians, the researchers demonstrated that tiny, systematic delays at certain points in the piece lead to the rhythm being perceived as swinging. The results help to better understand the mystery of jazz and can also help to make computer-generated music sound more authentic.
A swinging rhythm is considered one of the central characteristics of jazz. But what defines the swing? Musicology is still looking for an answer to this question more than 100 years after the emergence of jazz. According to previous findings, part of the explanation lies in the design of accented and unaccented beats, so-called downbeats and offbeats. Downbeat refers to the beats at which the conductor’s arm goes down and which are emphasized in the basic pulse of the piece. Offbeat refers to the beats between beats. But although computers can now imitate the correspondingly characteristic sequences of downbeats and offbeats, there is no swing feeling. So what is it that is missing?
Jazz in the lab
To answer this question, a team led by Corentin Nelias from the Max Planck Institute for Dynamics and Self-Organization in Göttingen carried out an experiment: the researchers manipulated original recordings of famous jazz pieces on the computer in such a way that the soloist’s playing was either exactly synchronous with the rhythm section or minimally delayed at certain points. Previous studies had suggested that tiny rhythmic delays can contribute to swing feel—but in a previous experiment the team did, such random timing differences tended to make a recording perceived as less swinging.
For the current study, Nelias and his colleagues therefore used the delays systematically: in one test condition, they delayed both the downbeats and the offbeats of the soloist in relation to the rhythm section, in another variant only the downbeats were delayed, while the offbeats with the rhythm section were in sync. The research team had professional and semi-professional jazz musicians rate the manipulated pieces, asking them to state how much they felt the piece in question swings.
Swing feeling due to delays
The result: While the subjects rated the completely synchronous version and the variant in which both the downbeats and the offbeats were delayed as little swinging, they rated the version in which the downbeats were systematically delayed by 30 milliseconds while the offbeats stayed in sync with the drums significantly more often than swinging – without being able to pinpoint exactly why. “The professional jazz musicians, whom we explicitly asked about at the end of the experiment, could hear differences, but could not identify these minimal deviations,” reports Nelia’s colleague Theo Geisel.
For the research team, this raised the question of whether jazz musicians themselves use the effect of delayed downbeats at all. To find out, they analyzed more than 450 solos by famous jazz musicians. And indeed: in almost all cases, the jazz professionals delayed the downbeats by a few milliseconds. “This subtle method of creating the swing feeling is apparently only used unconsciously by jazz musicians; they were not aware of the effect itself,” summarizes Geisel. Now that the study has revealed this secret of jazz, computer programs can potentially make use of it too. “Adding downbeat delays according to our findings can help improve swing capabilities for digital music production,” the authors say.
Source: Corentin Nelias (Max Planck Institute for Dynamics and Self-Organization, Göttingen) et al., Communications Physics, doi: 10.1038/s42005-022-00995-z