Why do orchestras tune to the same note?

A musical note is a frequency, measured in hertz, and what the ear registers as harmony is the ratio between frequencies rather than their absolute values. Two violins playing an octave apart sound right when one string vibrates at twice the rate of the other. If each player set their own reference, the ratios within each instrument would still be correct but the ratios between instruments would be wrong, and the result is the sour beating you hear from an untuned ensemble. So the orchestra fixes one anchor note and derives everything from it. The oboe traditionally supplies it: its penetrating timbre is audible over a full stage, and unlike strings it cannot simply be tightened or loosened at will.

The underlying principle is coordination. There is no acoustically privileged frequency for A. Surviving instruments and tuning forks show historical pitches ranging roughly from 400 to over 460 hertz depending on city, era and use, with church organs often far from theatre pitch. Any of these works internally. What does not work is two players choosing differently. A conference in London in 1939 recommended 440 hertz, and the International Organization for Standardization published it as ISO 16, reaffirmed in 1975. The standard is a convention agreed for interoperability, in the same family as screw threads, shipping container sizes and network protocols.

In practice the standard leaks. Many European orchestras tune sharp, commonly 442 or 443 hertz, in the belief that higher pitch gives a brighter sound, which drags string tension and instrument stress upward. Historically informed ensembles deliberately tune down, often to 415 hertz for Baroque repertoire, roughly a semitone below modern pitch, so that gut strings and period winds behave as their builders intended. Electronic tuners, keyboards and recording software default to 440 but nearly all allow the reference to be shifted. Wind instruments still warm up sharp, which is why tuning happens after the players have blown air through them, not before.

Common misconceptions persist. The myth is that 440 hertz was chosen for acoustic or physiological reasons. The reality is that it was a committee compromise between the pitches already in use. The myth that 432 hertz is a natural or healing frequency has no support in evidence, and the claim that Nazi officials imposed 440 hertz is unfounded. The myth is that everyone tunes to A. The reality is that wind bands commonly tune to B flat or F, because those are the instruments' home keys. The myth is that tuning happens once. The reality is that temperature and humidity shift pitch throughout a performance.