Metrical Dissonance
Metrical dissonance occurs when two or more rhythmic layers in a piece conflict with one another, creating tension against the notated (or implied) meter. Theorist Harald Krebs identifies two primary types. Grouping dissonance (labeled G x/y) arises when one layer groups the pulse in x units while another groups it in y units simultaneously — for example, a melody phrased in groups of three against an accompaniment phrased in groups of two. The familiar hemiola, where two measures of triple meter are temporarily reinterpreted as three measures of duple, is a common G 3/2 dissonance.
Displacement dissonance (labeled D x+n) occurs when a layer shares the same pulse grouping as the meter but is shifted by n beats, placing its accents between the bar's notated strong beats. A syncopated melody that accents the offbeats while the accompaniment reinforces the downbeat creates this displacement. In a simple 4/4 context, an accented upbeat pattern shifted by a half-beat (D 2+1) clashes with the downbeat layer, and listeners feel the pull between the two grids.
Both types of dissonance can operate at multiple metrical levels simultaneously. A passage might contain a surface grouping dissonance (triplets against duplets in a single measure) and a hypermetrical displacement dissonance (a theme that consistently enters one beat early relative to the hypermetric grid). Metrical dissonance is a powerful expressive tool: composers use it to generate rhythmic excitement, signal structural arrivals (by resolving dissonance at a cadence), or sustain tension across extended passages. Resolving to consonance — all layers aligning on the same strong beat — carries a satisfaction analogous to the resolution of a harmonic dissonance.
