Ivo, to je zaujímavá otázka...
Tu
http://pbosf.blogspot.sk/2010/01/story- ... pitch.html píšu dokonca, že A bolo regionálne rozdielné : "pitch levels as high as A-465 (17th century Venice) and as low as A-392 (18th century France)"
Teraz vraj "autentickí interpréti"
používajú 415Hz.
Podľa všetkého, ladenie sa zistilo pri skúmaní dochovaných nástrojov - hlavne organov :
http://www.piano-tuners.org/history/pitch.html
Scholars who have studied historical instruments claim that the pitch of the note "A" in the seventeenth century may have varied from 373.7 Hz to 402.9 Hz. The following is an incomplete list of pitch standards from various sources.
1640 Vienna Franciscan Organ A457.6
1699 Paris Opera A404
1711 John Shore's tuning fork, a pitch of A423.5 He invented the tuning fork, one of which still exists today.
1780 Stines, for Mozart, A421
1780 Organ builder Schulz A421.3
1714 Strasbourg Cathedral organ A391
1722 Dresden's chief Roman Catholic church organ A415
1759 Trinity College Cambridge organ A309
1762 Stringed instruments at Hamburg A405
1772 Gottfried Silbermann built the organ in the main Roman Catholic church in Dresden, and it had a pitch of A 415 at the time.
1780 Organ builder Schulz A421.3
1780 Stein's tuning fork A422.6
1751 Handel's own fork A422.5
...atď
resp malinko pod F ( F vyššie od E 
samozrejme)
