You may be astonished to hear this, but the term I have chosen for the title of this post is of my creation/invention. At least, if we can believe Google. The only similar uses they turn up have to do with image textures, not musical ones. So let me define my term!
Metric textures are a category of musical devices and practices having to do with rhythm, specifically meter, in music. Let's just review some basic terms. In music we talk about time in various ways. The timing of a piece of music refers to its duration in minutes and seconds: "what is the timing of the first track on the disc?"
Pulse refers to the repeating beat underlying the music, akin to the pulse created by our heartbeat.
Meter refers to how the pulses are grouped. This is indicated in a musical score by the time signature which in simple meters usually consists of two numbers: the upper one tells us how many pulses make up the metric group and the lower one what rhythmic value counts as a pulse. A typical example is the ubiquitous 4/4 time signature indicating four beats or pulses in each metric group with each beat a quarter note. There is another kind of time signature used for compound meters where there are two levels of grouping. In these meters the sub-group is usually three notes instead of the usual two, making the larger group a dotted note. Examples of these are 6/8 and 12/4. In musical scores the metric groups are normally divided off with barlines.
Rhythm refers to the pattern of short and long notes that we hear as the surface of the music. For example, each pulse or beat can be divided up into shorter notes that create subdivisions. The varying of these subdivisions is the rhythm of the piece.
There are certain music techniques that use layers of different meters to create interesting rhythmic effects. One of these is called hemiola and was a favorite way for Baroque composers to clinch an important structural cadence. It depends on re-grouping the meter. A typical example would be to turn the recurring dotted quarter pulse of a piece in 6/8 temporarily into 3/4 by rewriting the rhythm to group the patterns into quarter notes instead of dotted quarters. This changes the basic pulse. In flamenco a similar technique is used to create a polyrhythm or polymeter where we hear the two groupings simultaneously instead of sequentially. This is used in the flamenco palo known as bulerías. It is a bit tricky to show in notation, but it can look like this:
Or follow the link to the Wikipedia article. On one level, a measure of 6/8 is followed by a measure of 3/4, but on the other level a quick 3/8 continues throughout. Here is how bulerías sounds like in performance. What you hear are various slices of the metric texture, which is always present in the background, but not in the foreground.
This idea, of combining two different metric groupings, is an example of a metric texture. It is found in flamenco music, in African drumming and is the technique used in a lot of music by Steve Reich. Layering different meters creates a kind of sustained tension that enables him to write quite long pieces that seem to hover, almost without change, for long stretches. It is the built-in tension of the metric texture that makes the music exciting to listen to in the absence of the usual harmonic and melodic devices that music has traditionally used.
The first kind of metric texture used by Steve Reich came about through experimenting with tape loops. If you run the same tape loop at slightly different speeds, you get some interesting results as we can hear in the early tape pieces like Come Out from 1966:
As this technique, called "phasing" by Steve Reich, involves infinitesimal changes, it resembles a kind of metric calculus! Reich soon discovered that it could be adapted to use in compositions for live performance and Piano Phase is a simple example:
This is performed by two pianists both playing this pattern at the beginning together. Then one pianist slightly speeds up until he is one sixteenth-note ahead, at which point the two pianos synchronize their sixteenths. Then this process is repeated. What happens is a metric texture is created through minute tempo changes. Here is what that sounds like:
In another post I will look at some other examples of metric textures in Steve Reich.