eli5: in music, since there are 12 notes per octave, why are only 7 letters used instead of 12?
In: 15
You can make harmonic music with just five notes (the pentatonic scale). Our brains hear different frequencies that are simple ratios to one another as pleasant or “harmonic”. A 2:1 ratio is an octave, but other ratios like 3:2 or 4:3 are great, too. It turns out that when you multiply a base frequency (the “tonic” frequency, like A 440 hertz) by the 12th root of 2, eventually you can create most of these simple harmonic ratios with a close margin that our brains detect as harmonious.
Again, you really only need 5 notes, but musicians discovered that by including two extra tones in the scale they could create music that, while not as harmonious, was more complex and interesting.
It’s a mixture of how the math works, how our brains work, and the tastes of the founders of western musical traditions.
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