Orchestras tune to the A440 pitch. (theilr) / Flickr )
The sound of an orchestra tuning is instantly recognizable. As soon as you hear it, you know exactly what’s about to happen. But there is a simple reason why a whole lot of tuning orchestras sound awfully alike — they are tuning to the same pitch frequency, an A at 440 hertz* (abbreviated “Hz,” a hertz is the unit by which we measure frequency).
But that makes you wonder — how did they choose that particular pitch? Was there some kind of mega-music conference where the powers that be decided that A440 was to be the tuning standard? Yes. Yes there was. Several, in fact. Full story.