Variable beat division
Each of our examples so far has used only one meter, tempo, and way of dividing the beat. When these things change in the course of a piece, the change can often be indicated simply by writing a new “hurdle” with the appropriate figure(s) above it.
For instance, Ernst Toch’s “Geographical Fugue” for speaking chorus is written in a meter of four beats to the bar, initially with beat division by four; but after the first two bars, the rhythm changes to a steady stream of fast notes at a rate of six per beat. This can be indicated by writing a hurdle over the first beat of bar 3 with the new beat division indicated by the figure “/6.” Only the aspect(s) that change need be indicated: there is no need to repeat the previous figures for tempo and beats per bar, which still apply.
However, this simple approach won’t always work, especially where changes of beat division are involved. This is because changes of beat division often apply on a smaller scale: maybe just to one beat (as in an occasional “triplet”) or just to the melody and not the accompaniment. If we wrote the usual type of hurdle every time, we would have to keep writing additional hurdles to cancel these small-scale changes. Global notation therefore provides several different forms of hurdle, distinguished according to how much of the music they apply to.
The horizontal length of any hurdle indicates the unit of time to which the figures written above it apply. This is normally one beat, but it can be something else in the case of more complex time relationships such as five equal notes in the time of three beats.
If the score has only one layer, the hurdle forms applying to “all layers” are used to reflect the fact that no distinction is being made between layers.
To illustrate the use of different hurdles, let’s take the famous “Habanera” song from Georges Bizet’s opera Carmen. Here we give the rhythm of the melody with Oscar Hammerstein’s lyrics from his English version Carmen Jones. The habanera rhythm is based on two beats per bar with beat division by four, but Carmen’s melody occasionally divides a beat by three instead, as at the words “baby that.” As this triplet occurs only once at a time, it is indicated by a hurdle with only one horizontal line. After that, the beat division returns to the one indicated by the previous double-lined hurdle.
Next we’ll notate the rhythm of the accompaniment as well as the melody, using a separate layer for each. As the accompaniment is played staccato rather than sustaining each note until the next, we’ll notate it using the symbols for sounds of unspecified duration (see Articulation and melisma). The notation shows that while Carmen is singing her triplet, the accompaniment continues to use the characteristic habanera rhythm based on beat division by four (with onsets on the first and fourth pulses of beat 1), so in this case the change of beat division only applies to the top layer. To indicate that, the hurdle has its end lines pointing up instead of down.
Sometimes it may be necessary to distinguish different beat divisions used simultaneously within a single layer. This is especially likely when dealing with sounds of specified pitch, since global notation tries to represent all such sounds within a single layer wherever possible. One way of making such a distinction is to use different symbols for the different elements within the layer (for instance, for melody and accompaniment) and to indicate which symbols the change of beat division applies to.
The melody and accompaniment rhythms of Carmen’s “Habanera” song could be notated in a single layer by writing them above and below a single layer line, using symbols for sounds of specified and unspecified duration respectively. As the triplet applies only to the sounds of specified duration, the symbol for such a sound is written above the hurdle, before the “/3.” As the hurdle now applies to “all layers” (since there is only one layer), it reverts to the form with end lines pointing down.
The tempo and number of beats per bar don’t usually vary between layers in this way, but if they do, this can be specified in the same way as variations of beat division, with figures written over the appropriate form of hurdle. (The bar and beat lines may not line up between layers, but they will all be spaced according to a consistent time scale as usual.)
So far, we have assumed that each sound source uses only one kind of sound and playing technique. But there may be times when we want to specify contrasting sounds from the same instrument, such as strokes on the head and the rim of a drum, or to indicate which hand plays each stroke. To complete our initial overview of how to specify onset timing, we will consider some ways of giving such additional information when pitch and duration are unspecified.