Downbeat delays are a key part of swing in jazz

To what extent and how do jazz musicians synchronize their rhythm to create swing? Swing is a defining feature of jazz music, but its main psychoacoustic and musical components have remained elusive, except for the obvious long-short quarter-note subdivision. In particular, the possible role of microtiming deviations for swing has been the subject of long-standing controversy. Adopting an operational definition of swing, we present a study that ultimately demonstrates a positive effect of certain microtiming deviations on swing. We manipulate the timing of original piano recordings to conduct an experiment with professional and semi-professional jazz musicians measuring the swing of different timing conditions. We thus prove that slightly delayed upbeats and synchronized offbeats of a soloist compared to a rhythm section improve the swing. Analyzing a set of 456 jazz improvisations, we find that many jazz musicians use minute delays. These results show that systematic deviations from microtiming in the form of downbeat delays are a key element of swing in jazz.

"What is this thing called swing", is a question already raised by Louis Armstrong in a well-known song. The phenomenon of swing is certainly one of the most salient general characteristics of jazz music and is considered an essential ingredient of jazz performances. The term was introduced by jazz musicians to describe what they considered a specific playing style in their performances. Yet surprisingly, a century after jazz musicians like Armstrong and Ellington hit the scene, the nature of swing and its main musical and psychoacoustic components are still controversial. It has even been argued in the past that "you can feel it but you just can't explain it"1, or similarly, according to the New Harvard Dictionary of Music, that swing is "an intangible rhythmic momentum in Jazz. Manifested specifically in a variety of relationships between long and short notes, or in the presentation of single notes, swing defies analysis”2.

Among the possible components of swing, only one has been unambiguously established so far, the unequal subdivision of quarter notes into long and short eighth notes. It is measured by the so-called swing ratio, i.e. the length ratio of consecutive long and short eighth notes called highlights and mishap. (Downbeat refers to the first eighth of a quarter note, offset to the second eighth. An interactive tool with audio examples demonstrating downbeats, offsets, and different swing ratios can be found on our website (https://www. ds.mpg.de/swing/swingratio) Non-experts can also find a brief description of relevant music nomenclature in Supplemental Note 1.) Listening to computer-generated jazz music that has been "swingified" by putting Simply implementing a swing ratio ("swinged notes")3, it is obvious to jazz musicians that this is not enough and that there must be other components. But who are...