The question of Frequency.

A bit of information about the unitarian agreement and standardization of 'Concert tuning"  world wide.
This is one story, telling aspects of the changes, however more research is needed to  try and understand the whole story.

I ask WHY is it standardized at all?
Of course acoustic pianos, with the amount of piano wires needing attention, would have to choose to tune all 'strings' relative to either A440 or 432.
Guitars and other string instruments have the options to change for their liking with consideration  to limits on individual strings available for guitars.  Tuning such string instruments have more flexibility to change tunings.
The Human Voice does not have to adhere to the dictates of the Globally agreed frequency and can function as it's own physical body vibratory aspects. 