Metric modulation is the modulation of the original metre, either upwards to a faster tempo or downwards to a slower tempo, using a subdivision of the original pulse to decide the speed of the modulation. The mechanics of the process are as follows:

1) Subdivide the original pulse into smaller or larger pulses.

2) Reorganise these pulses into regular groupings, so that the impression of a new tempo or metre is created.

However it should be stressed that at no time during Examples 9 -17 does a real new tempo come into existence, only the impression of a new tempo is created. This "new" tempo maintains a strict relationship to the original pulse at all times. This type of metric modulation is a very common one, and is probably one that you have done yourself at times. A simple example of metric modulation is the technique of "double time" and "half time". When we go to double or half time we maintain a strict relationship to the original pulse and the changes go by at the original speed. This is metric modulation. In double time the modulation speeds up, and in half time the modulation slows down. The technique of metric modulation can be used extremely effectively to create tension and release, and to provide variety and contrast within a piece.

In the written part of the examples, everything is written out rhythmically only. On the two stave system, the bottom stave represents the original pulse and the top stave represents the modulation. On the top stave, the dotted line represents the bar line of the new suggested pulse.

All of these subdivisions are of 4 or 8 bar lengths. The reason for this is that as jazz musicians we are used to dealing with tunes constructed from these numbers of bars and when dealing with an unfamiliar concept like metric modulation it is good to have something to relate to. However I must stress that modulations can last for any length of time and, like substitute chord changes, are completely at the discretion of the improviser.

In all of these examples, when the bass and drums modulate to the new tempo, both instruments accentuate beats 2 and 4 of the bar in the normal jazz manner. All of these examples are of swinging time but there are of course other ways of modulating with different feels.

The basic process of these modulations is as follows. Take the original pulse and subdivide it, (such as into quarter note triplets as in example 9), and then, treating each single unit of the subdivision as a quarter note, regroup these subdivisions into 4, thus creating the impression of a new tempo but in reality being part of the original tempo.
 

Example 9: 6 bars modulated pulse = 4 bars original pulse. Modulation: 3 over 2

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On to Lesson Six

Odd metres.

Demonstration Composition

A compostion using various techniques described in the book.

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