One way you can use music theory to add rhythmic interest and variety to music is through the use of irregular rhythms (also called irrational rhythm or artificial division). An irregular rhythm is any rhythm that involves dividing the beat differently from what’s allowed by the time signature.
The most common of these divisions is called a triplet, which is three notes joined together that equal the beat of a single note. The second most common type of irregular rhythm is a duplet, which is two bracketed notes with a note value of three of the same notes.
Irregular note divisions, such as triplets and duplets, allow for more complex rhythms than “regular” notation time normally allows.
Adding interest with triplets
Say you want to put a quick little sequence of three notes where you’d normally play one quarter note. In 4/4 time, if you want to play an even number of notes in your sequence, you can use a couple of eighth notes, or four sixteenth notes, or eight thirty‐second notes. But what if you want to play an odd number of notes, and you absolutely want that odd number of notes to equal one beat?
The answer is to play a triplet, which is what you get when you have a note that’s usually divisible by two equal parts divided into three equal parts.
A good way to count out the beats while playing triplets is to say the number of the beat followed by the word triplet (with two syllables), making sure to divide the triplet played into three equal parts.
For example, the measures would be counted off like this:
ONE two THREE triplet four ONE triplet two THREE triplet four
You can show the triplet notation in two ways: with the number 3 written over the group of three notes or with a bracket as well as the number. Read triplet notation as meaning “three notes in the time of two.”
Working with duplets
Duplets work like triplets, except in reverse. Composers use duplets when they want to put two notes in a space where they should put three.
An example would be dividing a dotted quarter note into two eighth notes instead of three eighth notes as you would in a measure of music under a compound time signature. A good way to count duplets is to count the second note in each pair as and instead of assigning it a number value as you would any other beat in compound meter.
You count the measures like this:
ONE two three FOUR and ONE and FOUR five six
