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by Phrodo_00
590 days ago
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It's pretty much historical, and initially based on the tastes of medieval priests doing Gregorian chant. It started with the handful of intervals they would use and more intervals were added as needed when music grew more complex until we got to similar-ish 12 intervals, which were then actually equally spaced later. |
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https://22shruti.com/
Indian music theory identifies an octave 7 notes, which are modified further to make 12. Beyond these 12 some of them have finer divisions that map onto an underlying 22 tone system.
This diagram summarizes it:
https://22shruti.com/wp-content/uploads/2023/03/revised-evol...
Notice something peculiar. The P note which corresponds to perfect fifth in western theory, is the same through those layers. It does not split into multiple fine or grain pitches.
Those pitches that we would identify as flat fifths are related to M, not P. And in fact, jazz theorists take a similar view: that in many contexts flat fifths are actually augmented fourths, related to the Lydian.
To make a 7 note scale, you would need an M. In the 12 tone layer, there are two flavors of it: M and m. Something analogous to your perfect fourth and augmented fourth. Then each of these has one of two possible representations in the 22-tone layer. The P is always just P.