At what point in history did the relationship between pitch and frequency become well-known among musicians?

Question

I think I've read that even very ancient cultures were able to discern that an octave difference corresponded to a pipe of twice the length, and so on. But at what point were musicians and composers able to understand that each note in a scale of fixed notes represents a certain number of Hz?(I'm interested in facts relating to various areas - if it was known earlier in Vanuatu than in Vienna, I'm interested in that level of detail!)

Answer 1

The unit “hertz” (Hz) as an expression of the number of times (frequency) that a repeated event occurs per second (cycle per second) was established in 1930 by the International Electrotechnical Commission, and so called in honor of the German physicist Heinrich Rudolf Hertz (1857-1894). The frequency of the note A₄ was fixed to 440 Hz during an international conference in London in 1939.

But the first explicit references to a correlation between frequency and musical pitch were made by the French mathematician and physicist Joseph Sauveur (1653-1716), who developed a first system to determine the exact pitch of a note expressed in cycles per second. He has been also credited with coining the term "acoustique".

The first time a reference pitch was set by an official decree was in France as well, when, on February 16th 1859, it was determined that a “normal A” would correspond to 870 cycles per second (= an octave higher than current A₄ tuned at 435 Hz).