First, some niche Twitter comedy:
Twelve-tone equal temperament is socialism, Make Intonation Just Again
— Dr Ethan Hein (@ethanhein) June 26, 2020
The Well-Tempered Clavier is a book of JS Bach compositions for keyboard instruments in each of the twelve major and twelve minor keys. The name refers to Bach’s preferred tuning system, which made it possible to play (sort of) in tune in every key. This was a big deal, because in the usual tuning systems of Bach’s era, only some of the keys sounded good, while others sounded horrible. The history of tuning in Western music is complicated and abstruse, and I won’t go into detail about it in this post, but you can learn some of how it works here. The key facts:
- Western tuning systems, keys and scales are based on the natural harmonic series.
- Harmonics are based on prime numbers.
- Prime numbers don’t divide into each other evenly.
The practical consequence is that your music can either be in perfect tune, or it can use more than one key, but it can not do both. In Hindustani classical tradition, they opted for being in tune, so everything is in a single “key” defined by the omnipresent drone. Western Europeans wanted to be able to change keys, however, and that required some tuning compromises.