Polyrhythm Metronome

A polyrhythm sets two evenly spaced pulses against each other in the same stretch of time, such as three beats against two. It is a feature of West African drumming, Latin and jazz music, and of classical piano pieces where the hands play different rhythms. It is hard to feel at first because the beats do not line up, and a metronome that plays both layers is the best way to learn it.

How the cycle works

Pick the number of beats for the first layer, A, and for the second, B. The page spreads A evenly spaced clicks and B evenly spaced clicks over one cycle, which has a length set by the tempo and the number of beats in the cycle. Both layers start together on the first step, which has the accent: a higher pitch than either layer alone. Then the layers drift apart and meet again at the start of the next cycle.

A worked example

Press Sample: 3 against 2 at 60 BPM, with a cycle of 4 beats. A beat lasts a second, so the cycle lasts 4.00 seconds. Layer 1, the high click, plays three times, 1,333 ms apart; layer 2, the low click, plays twice, 2,000 ms apart. The shared grid is 6 equal steps, the least common multiple of 3 and 2, and the layers meet only at step 1. There are 5 clicks in a cycle. Counting the six steps, the three-beat layer falls on steps 1, 3 and 5, and the two-beat layer on 1 and 4.

Learning a polyrhythm

Start slowly, around 40 BPM, and listen to the two layers together. Then mute one and tap the other with a hand, add the second layer with the other hand, and unmute. The shared grid is the key: count it out loud as one-and-a-two-and-a-three and place the beats on the numbers. Presets for 3:2, 4:3, 5:4, 7:8, 5:3 and 7:4 let you move on to the harder ones.

The controls

The two number fields set the layers from 1 to 16. The tempo slider sets the underlying pulse from 20 to 200 BPM, and the one-cycle option sets how many of those beats it contains: 1, 2, 3, 4 or 8. A longer cycle at the same tempo slows the layers. Mute the high click or the low click to hear a layer on its own. The display below shows both layers and lights each beat as it sounds.

Timing

Each click is scheduled on the browser’s audio clock a short time ahead, so the timing does not wander when the page is busy. The lit beats follow with a small delay and are only a visual guide. If the sound on your device is delayed, for example on Bluetooth speakers, the clicks arrive late but still evenly spaced.

Edge cases

Ratios with a common factor, such as 4:2, sound like a simpler ratio, here 2:1, but the page plays exactly the numbers you enter, and the layers coincide more often. Large numbers produce a long shared grid and many clicks, so a 7:5 at a fast tempo is very dense. The tempo is for the underlying pulse, not for either layer, and the layers may be faster than the BPM suggests.

Limits

It plays clicks only, with no accent patterns beyond the shared downbeat, and no subdivisions or swing. Settings are saved in your browser, and the sound is generated locally.

Related tools

• Tap Tempo finds the tempo to use as the underlying pulse.
• Metronome plays an ordinary beat with accents.
• Delay Time Calculator turns tempo into note lengths in milliseconds.
• Tone Generator makes test tones when you need a single pitch.