In Part 1 we looked at where rhythm lies on the frequency spectrum, and what function it serves in comparison with the main branches of harmony. In this part, we’ll lay some fundamental groundwork in terms of rhythmic perception.


What we perceive to be the pulse, is our rhythmic ‘tonal center’, the ‘root’. 

All the subdivisions we build from this pulse we perceive as ‘harmonics’ from that root, like finer details of the main structure.

Perception of a main pulse can be affected by many things. It could be that the loudest, most regular rhythm being played is heard as the main pulse. It could be the rhythm played by the lowest pitched instrument (bass drum). It could also be felt differently from one person to the next, depending on their natural tendencies (one person may prefer to hear slower pulses, another fast), or even just what lies nearest to the indifference interval1 (around 100bpm).

If complex harmony was messy on the bass, going even further down to rhythmic frequencies you could expect that it’ll probably be even messier down here. You wouldn’t be completely wrong, but that doesn’t mean we can’t have a bit of fun.

Triplets are the equivalent of a perfect fifth from our ‘root’ (if you have no idea what I’m talking about here, check out this overview, or this video). If we play a three against two (3:2, ‘3 in the space of 2’) polyrhythm, we have the harmonic equivalent of a perfect fifth, with the root being the ‘2’ side of the polyrhythm.

3:2 polyrhythm: ‘root’ on the bottom, ‘5th’ on top

With note rates in this close proximity to one another, the effect can be of an ambiguous pulse. You could easily flip your perception to hear the triplets as the pulse, and the ‘2’ side of the polyrhythm as going against that, making a 2:3 polyrhythm. This might be exactly the point, as a lot of music plays on this ambiguity, and the feeling of drifting between one time perception and another.

Classic example of an afro-cuban bell pattern in 6/8, flipping the perception of pulse from 6/8 to 3/4

Example: Tap your foot on the numbers, and clap on the bold parts. See if you can flip your perception to feel either side of the polyrhythm as the main pulse.

  • Count “1-trip-let-2-trip-let” to hear 3:2
  • Count “1-and-2-AND-3-and” to hear 2:3

If you’ve ever seen visual illusions like the one below, this is essentially the same effect. Depending on whether you focus on the black or the white, you either see a vase or two faces. If we wanted to reinforce one image (pulse) over the other, we could give it more detail to make the image stronger, or simply draw attention to it.

The additional detail on the left draws more attention to the vase’s side of the illusion.

Adding rhythmic detail to emphasise a certain pulse can come in many different flavours. We could orchestrate one side of the polyrhythm on multiple voices/instruments. The increased volume and texture would draw more attention to it. But even keeping the dynamics level and alternating two voices for example, would pick it out; if you alternated the ‘2’ side of the polyrhythm to go between kick drum and snare drum you would feel a strong pulse or groove on that side of the polyrhythm. (More on why this works later.)

3:2 polyrhythm with Kick/Snare alternating on the ‘2’ side

Another way to add detail is to use subdivisions. These can add variety to a rhythm while reinforcing it. For example, instead of just playing X— X— for the ‘2’ side, playing X-xX-x makes a very strong pulse on that side.

Embellishing the Kick/Snare rhythm to make a ‘shuffle’ groove, emphasising the duple pulse.

Playing X-xxX-xxX-xx on the ‘3’ side would make a very strong pulse there.

Embellishing the hi-hat pattern to draw more attention to the triple pulse

Before we go on, a small note on timbre/texture.. Unless you’re playing a pure sine wave on a synthesiser, any musical note will be made up of not only the frequency of the pitch (the fundamental frequency), but a number of additional multiples of that frequency, all at the same time. This principle is known as the harmonic series, and these multiples and their various intensities give an instrument it’s sonic character/fingerprint. It’s how you tell a trumpet from a piano, or John from Jane. It’s the detail in the sound, that embellishes a certain frequency, making it clearer, more interesting, invoking a certain expression, emotion, character, cultural significance… you get the idea.

By adding subdivisions of a pulse, we’re adding detail, ‘harmonics’ to our original pitch. The musical vocabulary you use to add this detail creates a certain texture (for example playing the same drum groove with either a hi-hat ostinato of X-xx or Xx-x), but functionally serves the same purpose, and adds the same harmonics in relation to its ‘root’.

Simple 4/4 beat with varying semiquaver textures

In the case of the previous example that used alternating kick drum and snare drum to emphasise the ‘2’ side of the polyrhythm, another reason for the emphasis was that we had essentially added a lower harmonic to the crotchet pulse; both drums individually are now playing an ‘octave’ lower, each playing at the rate of minims (1/2 notes), just out of phase with each other.

So you can see how we can change the perception of what the pulse is in a piece of music, by using rhythm and subdivisions. This is the basis for fairly commonly used effects like metric modulation and rhythmic illusions. Changing this perception, and thus the underlying flow of the pulse, can have a dramatic effect on the feel and direction of a piece of music.

[more examples to come!]

Great. So what now?

All this is nothing new in itself. What I’m proposing is that we can take this different viewpoint of rhythm, and ask what else can be done with it? How can we see rhythm in a more melodic and harmonic way, and what music might you end up with as a result?

Check out part 3 for some practical applications, and ideas to build on.


1: https://www.oxfordreference.com/view/10.1093/oi/authority.20110803100001620

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