[rdtennent]

>Bach wrote The Well-Tempered Clavier to show off how one well temperament system (no one knows which one) sounds okay in every major and minor key. The keys closer to C sound sweeter and more euphonious, while the more distant keys sound darker and edgier.

Fairly recent research has shown that Bach may have been very explicit in specifying a temperament system. A series of what appear to be decorative swirls at the top of the title page of the WTC has been conjectured to actually be instructions for tuning to the temperament system he favoured.

[ethanhein]

I wrote a blog post summarizing this research. The idea is that the swirls specify turns of the tuning pegs to modify meantone temperament. It's more or less pure speculation, but it does produce a very nice-sounding tuning, almost equal temperament but not uniform across the keys. https://www.ethanhein.com/wp/2020/what-does-the-well-tempere...