Metric Modulation
A tempo change that does not sound like one. One note keeps exactly the same speed while the pulse underneath it is reinterpreted, so the music arrives somewhere new without anything appearing to accelerate. Listen to the pivot note here: it never changes.
- the pivot note
- same speed, new meaning
- no audible jump
which styles use it
- Prog
- Contemporary classical
- Drum and bass
- Jazz
In short
Pick a note value that exists in both tempos, for example a triplet eighth in the old tempo and a plain eighth in the new one. Keep that note running at its original speed and redefine the beat around it. The listener hears continuity because the fastest layer never wavers, and then discovers they are somewhere else entirely.
It is the rhythmic equivalent of a key change that nobody notices until it has already happened, which is exactly why composers who use it tend to use it a lot.
How to count it
- Find a value both tempos share
That is the pivot, and everything depends on it.
- Hold the pivot absolutely steady
Any wobble and the effect becomes an ordinary tempo change.
- Let the new pulse establish itself
Give the listener at least a bar in the new tempo before you do anything else.
Where you run into this
- In twentieth century concert music, where the technique was formalised.
- In prog and math rock, where it is used to shift a song sideways mid riff.
- In drum and bass and footwork, where halving and doubling the felt tempo is standard practice.
Our own examples
One groove at 120 bpm with triplets running, modulating so those triplets become the new eighth notes at 180. The pivot note is soloed first so you know what to follow.