The opposite situation is what Krebs calls metrical dissonance.I will argue that in jazz styles where swing rhythm is pervasive, halvingthe prevailing note-value can produce metrical dissonance, and that this dissonance is one of the main factors contributing to listeners’ perception of double time.To consider the idea of swing eighth notes in terms of Krebs’ metrical layers, I will callthe quarter-note level of rhythm the “beat layer” and the level at which quarter notes have been subdivided into swing eighths the “sub-beat layer.” The beat layer and sub-beat layer can be regarded as two different ways of grouping a third layer of

Music theorists have long been aware that different levels of beat are often simultaneously available to the listener. Harald Krebs (1999) uses the term “metrical layers” to describe this phenomenon. In the normal case, metrical layers nest neatly insideone another; they are metrically consonant with each other. This occurs, for example, in Pachelbel’s Canonas the prevailing note-values are repeatedly halved. Figure 3.1 shows this nesting relationship between layers. There is no need for a separate micropulse layer because the layers are metrically consonant: both eighth notes and quarter notes can be expressed as groupings of sixteenth notes.