Onset timing with more than one layer
We now know how to specify onset timing in relation to bars and beat division within a single layer (see Bars, Beat division). But most music has more than one rhythm sounding simultaneously, and to notate that, we will have to be able to specify onset timing in more than one layer. Fortunately, this is no more complex than what we have done so far: the layers are simply stacked one above another, with their beat and bar lines aligned.
The drum kit in a rock band, for example, contains a minimum of three sound sources - bass drum, snare drum, and hi-hat cymbal - each usually producing a different rhythm. In the standard “rock ’n’ roll” drumming pattern, for instance, the hi-hat cymbal plays a continuous stream of pulses dividing the beat by two, while bass drum strokes on beats 1 and 3 alternate with snare drum strokes on beats 2 and 4. Remembering that for sounds of unspecified pitch our default procedure is to use a separate layer for each sound source (see Sound sources), we could notate this pattern in three layers.
Although these instruments produce sounds of indefinite pitch, the layers are stacked in order of approximate pitch range, with the highest-sounding instrument at the top and the lowest at the bottom. To show that the three layers are sounding simultaneously, a continuous bar line extends through all three layers at the beginning. Otherwise, the bar and beat lines are broken between layers to keep the layers distinct.
In a one-layer score, the bar lines extend above the height of the beat lines, but in a multi-layer score they do so only in the top layer. This allows the layers to be placed closer together, saving space and therefore eye movement. (The bar lines still extend beyond the layer lines in each layer, to make it clearer where each bar begins.)
Saving space is always a good idea where we can do so without losing readability. Multiple layers can easily swallow up a lot of space, but we can often save space by using fewer layers. This makes sense especially when more than one sound source is deployed by the same musician, as in the case of the drum kit.
By using the space below as well as above a layer line, and by moving some of the layer lines closer together, shown below, we can produce a more efficient “condensed” score that gives the same information in less space. In effect, we are now notating all the sounds of the drum kit in a single layer (with a double layer line). Accordingly, the beat and bar lines are unbroken.
It might be suggested that we could save even more space by using a single layer line and placing the symbols above, on, and below the line; but this could create confusion because symbols placed on a line indicate sounds of specified pitch; see Specified duration and Specified pitch.
For more complex examples of multiple sound sources producing different rhythms, it may be clearer to stick to using one layer per sound source. By way of illustration, the percussion parts in a performance of a Brazilian toada de moçambique (Catholic festival song) might produce five different rhythms simultaneously.
The music is more complex than our examples so far, but the notation does not involve any new concepts or symbols. The one surprise might be the indication of specified durations in the tambourine part, which is explained by the fact that these refer to sustainable “shakes” of the tambourine.
We are now able to notate multiple rhythms happening either sequentially or simultaneously within the same piece of music, provided all the rhythms are based on the same meter, tempo, and beat division. But these things are liable to change in the course of a piece, and beat division can also vary between layers sounding simultaneously. We therefore need to be able to specify variations in tempo, meter, and especially beat division.
Sources
Brazilian toada de moçambique percussion score based on staff notation in:
Reily, Suzel Ana. 1998. Brazil: Central and Southern Areas. In Dale A. Olsen and Daniel E. Sheehy, eds, The Garland Encyclopedia of World Music, Vol. 2: South America, Mexico, Central America, and the Caribbean. Pp. 300-322. At p. 314.