Metric Modulation

     Tempo can also be modulated just as you can modulate to a different tonality. That can be achieved by simply performing a given musical passage in a faster or slower tempo, or even gradually change the tempo (Ritardando or Accelerando). This is called a metric modulation, because tempo is altered in the course of the music.

     But a given musical passage can be perceived as being played slower or faster even when the tempo doesn’t actually change, as if it was an illusion giving you the impression that there was a shift to a new tempo. Basically, one way of doing it, is to introduce a different rhythmic subdivision that contrasts with the one you were using before – this is called an Implied Metric Modulation.

     You can shift the natural, or expected accents, of rhythmic figures groups to give the impression of a metric modulation. In the example below, you will feel the contrast from shifting between sixteenth notes and eight note triplets with a shifted accent:

In this example we are changing the accent of eight note triplets to every 4 notes, instead of every 3 while maintaining the same basic rhythm

     Implied metric modulations can also be achieved by playing polyrhythms and this device can be used as a way of capturing the attention of listeners, adding variety or preparing a modulation to a new tempo:

Here we are using a 5:4 polyrhythm to give the impression of speeding up the tempo – kick and snare in quintuplet subdivision and hi-hats on a four note per beat subdivision