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How to calculate time signatures for polyrhythms?
Old 12th July 2020
  #1
How to calculate time signatures for polyrhythms?

I've got a theory question, and hopefully this is the right sub-forum for this.

I want to put together a polyrhythm with two different drums - one 6 beats to the bar, and one 9 beats to the bar.

I used this online polyrhythm generator to give me ideas about which combinations might sound best: https://mynoise.net/NoiseMachines/polyrhythmBeatGenerator.php

How might I calculate the time signature for this so I can set my DAW time signature correctly?
Old 12th July 2020
  #2
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denstrow's Avatar
You could set it to 3/4 (using 8ths) and the collective downbeat will be every 3 bars.
Old 12th July 2020
  #3
Quote:
Originally Posted by denstrow View Post
You could set it to 3/4 (using 8ths) and the collective downbeat will be every 3 bars.
Ah, OK. That makes sense. I suppose for anything where the beats aren't divisible by each other, I'll set the time signature around the one with the least beats-per-bar.
Old 13th July 2020
  #4
I'd set the DAW tempo to the dominate rhythm, which ever one "feels" like the main pulse. If neither is dominant, do whatever
Old 13th July 2020
  #5
Gear Addict
 
denstrow's Avatar
a/x & b/y is the basic formula

where a, b = rhythmic division, e.g. 4 divisions per beats=16ths, 3 = triplets etc, and x, y the superimposed rhythm

X times Y equals the number of beats it takes to reach a collective downbeat.

Set the time signature as you like, it doesn't matter.

For example:

4/3 + 4/7 (polyrhythm) -> 3x7=21 beats for the collective downbeat.


3/4 + 4/5 (polypulse) -> 4x5=20 beats for the collective downbeat.
Old 14th July 2020
  #6
Quote:
Originally Posted by denstrow View Post
a/x & b/y is the basic formula

where a, b = rhythmic division, e.g. 4 divisions per beats=16ths, 3 = triplets etc, and x, y the superimposed rhythm

X times Y equals the number of beats it takes to reach a collective downbeat.

Set the time signature as you like, it doesn't matter.

For example:

4/3 + 4/7 (polyrhythm) -> 3x7=21 beats for the collective downbeat.


3/4 + 4/5 (polypulse) -> 4x5=20 beats for the collective downbeat.

Ahh, this is excellent. Makes more sense now, and playing with the maths will help give me ideas
Old 27th July 2020
  #7
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Bob Ross's Avatar
 

Quote:
Originally Posted by EasyToAssemble View Post
I want to put together a polyrhythm with two different drums - one 6 beats to the bar, and one 9 beats to the bar.
First question: Are the bars of equal length/duration? Or are the subdivisions -- the individual 1/6th and 1/9th from your two beats -- of equal length/duration?

If the former, you are indeed talking about a polyrhythm...but then the second question immediately becomes: Is it 6 beats in the space of 9 beats (6:9), or 9 beats in the space of 6 beats (9:6)?

The composite rhythm of those two examples will sound identical as an isolated event...but the answer to that second question will determine what the primary underlying pulse should be, and that will tell you what your time signature needs to be.

But if the answer to the first question is the latter -- subdivisions of equal length/duration -- then you're not talking about a true polyrhythm, you're talking about a polymeter. Which opens up a different set of questions...
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