I was once riding on a bus with a pal, and the bus had a squeaking part. I said, "I wonder what that is," and she replied, "It's D."

That's perfect pitch.

I have read that perfect pitch is more common among people whose language uses pitch. By that I mean that in that language, when a person says a word high it means something different than if that person says the word low. Since pitch conveys meaning, speakers pay attention to it when very young, and apparently they develop perfect pitch that way.

As for those who suffer when people are singing low or high, I say "get over it." People can sing beautifully together without imitating lifeless instruments.

I read a book by James Galway, the famous flautist, and he said that the idea that A = exactly 440 is wrong. Pitch is highest in Germany and lowest in the United States.