Credits:
Photographers:
Xavier Mignon, Veronique Alfieri,
Michael Baumgartner, Thomas Reban,
Herbert Heim
Early Music Source is an excellent site with plenty of very useful musicalities
and own youtube channel
Pythagorean Basics:
an American popularization
Jazzduets is an interesting site about improvisation
a very rational explanation of tunings:
Pythagorean tuning, Just intonation, the Meantone temperament, and finally – the equal temperament