Despite what is widely believed, there never has been and probably never will be a universally agreed and used pitch standard for music. As a small example, there are still many Victorian church organs in the UK that play at their original ‘Old Philharmonic’ pitch – about a quarter of a tone higher than today’s theoretical norm of A440. And several famous orchestras play just a bit higher than that as well.
Even older organs and other instruments tell a story of great diversity. Bach worked at two pitch standards on a daily basis, Handel owned a tuning fork that gave yet another and for musicians in Monteverdi’s time and place the pitch standard was about a semitone higher than A440. So this is the pitch at which we will perform.
But there is a second pitch issue with the 1610 Vespers. The fifth psalm Lauda Jerusalem and the Magnificat appear to sit very much higher than all the other music. At Monteverdi’s pitch singers would definitely feel under pressure in these movements. But this appearance is deceptive and help is at hand. Music theory and notation at the time were such that composers wishing to write music in certain ‘keys’ had to write it four notes higher using a combination of clefs that contemporaries would have recognised as ‘requiring transposition down’. So we will. What a relief!