Definition
It is the speed at which chords change and the way the changes are distributed in time. It is independent of BPM: a piece at 160 BPM with one chord every four bars has a slow harmonic rhythm.
Principles
- Acceleration toward the cadence: one chord per bar, then two, then the cadence. In C: | C | Am | F G | C |.
- Changes on strong beats: they stabilize. Early changes (on the last eighth note of the preceding bar) create drive: this is the typical anticipation of pop, funk and K-pop.
- Contrast between sections: slow verse (| C | C | F | F |), denser chorus (| C G | Am F |) or the opposite to let the chorus “breathe.”
- Harmonic rhythm and melody: if the melody is very active, the chords can stay still, and vice versa.
A tool for emphasis
In songwriting courses at Berklee harmonic rhythm is a highlighting tool: slowing the changes under the title of the song makes it stand out; speeding them up in the pre-chorus creates urgency.
In genres
- Trap and rage: often one chord or a two-chord loop for eight bars; the interest lies in the rhythm and the sound.
- Jazz and gospel: even two or four chords per bar.
- Classical music: slowing at cadences, acceleration in developments.
Real example
Bach's Prelude in C BWV 846 changes chord exactly once per bar: the constant harmonic rhythm becomes the very form of the piece. At the opposite extreme, “Get Lucky” by Daft Punk repeats a four-chord cycle at constant speed throughout the track, and the variation is left to the arrangement.