Audio: microtonality (0:08)
microtonality plays microtonal music. The microtonality figure shows the score:
Whilst 12TET is the most widely used tuning system for writing music, equal temperament tuning can be used to divide an octave into any number of notes.
Writing microtonal music is a matter of deciding which tuning system to use, devising a scale or scales to use from that tuning, and then deciding the rules for writing melody, chords and chord progressions.
24TET is one of many microtonal tunings and it is used to write microtonality. It has 24 notes in an octave. It is an interesting tuning because it includes all the 12 notes of the chromatic scale found in 12TET. 24TET can be used as a sort of expanded 12TET with half the notes, the microtones, acting as the equivalent of blue notes or bent notes between the chromatic scale notes in 12TET.
All sorts of scales can be created in 24TET in the same way as different scales and modes are created in 12TET. One popular option is to devise a micro version of just intonation, such as 11 limit tuning, which works well in 24TET. Another is to simulate an existing scale that is difficult to reproduce in 12TET, such as the pentatonic slendro with five notes or one of the many Arabic scales. A further option is to use all 24 notes as a sort of extension of the chromatic scale in 12TET. A further option is to experiment and create a new scale without a 12TET counterpart. The scale in the second half of microtonality is such a scale. It is octatonic with eight notes, and the interval between successive notes is three microtones. Its nearest equivalent in 12TET is the diminished scale.
Harmony is the most challenging part of microtonality. There are lots of ways to construct chords and to link them together in a progression and no rules to guide you. The second half of microtonality builds chords using the interval of three microtones. Chords are limited to three notes and can be complete or incomplete, in root position or inverted, and voiced in open or close harmony. The only rule, taken from voice leading, is that a common note is voiced in the same part. The chords were generated randomly by selecting a number between 0, the tonic, and 23, to determine the chord root note. Chord progression, root movement from one chord to another, is entirely the product of chance.
24TET represents the tip of an iceberg. Underneath the surface there is a wealth of detail to explore. There are simpler systems such as 5TET and 7TET which contain five and seven notes respectively. 15TET has 15 notes, 19TET has 19 notes and, if these are not enough, you will be pleased to know that there is a 171TET. There are even scales based on intervals other than the octave such as the Bohlen Pierce scale. This comprehensive list of intervals details the name and frequency ratio of around 250 intervals in just about every tuning imaginable.