Today, concert pitch A is 440Hz. Why is it 440Hz? That’s an easy one… back in 1939, a bunch of guys with a bunch of education got together, talked about it for awhile, probably there was some shouting involved at one point, no doubt someone left mad and basically they decided to plop their “A” down at 440Hz. Oh, those wacky scholar types! It should be noted that there was a big, nasty war that ripped through Europe right after this; some people just take stuff way too seriously.
So, you ask, what was it before that? I’m glad you asked that! In the past, the note “A” has been defined everywhere from 466Hz (A#/Bb of today) all the way down to what we call “G” today — 392Hz. (I’ll leave off the joke; it’s far too obvious.) So, for the couple of hundred years before 1939, note pitch was jumping around all over the place. This caused problems for musicians when they went on tour and also resulted in more than one bar fight, probably over the suggestion that pitch jumped around so much so that the harp players wouldn’t have to constantly retune.
But, what is the real reason for pitch snaking around up and down the scale? To oversimplify some, throughout history notes have been defined according to the tuning fork of whoever happened to be the most prestigious musician at the time.
So, “A” is 440Hz now and it’s going to stay there and we can all move on to better things, no? Well… No. Some orchestras are tuning their piano to A446; The Chicago Symphony tunes to A442. Can a person really hear the difference between A440 and A446? Pretty much. Is it enough to get bent out of shape over? Only if you make your living in the halls of academia (and they make an ointment for that).