During a recording session on Saturday, I kept hearing tuning issues between the acoustic guitar and the keyboard. The keyboard player was using a Wurlitzer patch and I thought that the patch might have been using a de-tuning effect.
After several recording passes, it was very clear to me that we still had tuning issues. We finally discovered the mystery: the acoustic guitar player had inadvertently recalibrated his tuner to A444 instead of A440.
I was asked a question about the history of A440 as a reference standard for tuning instruments. And here is what I discovered.
From the 17th century forward the reference note A has ranged from a low of 373.7Hz to a high of 457.6Hz. The differences can be loosely described this way: a lower tuning results in a darker sound, while a brighter timbre is attributed to a higher tuning. In 1936 the American National Standards Institute adopted 440Hz. In 1939 A440 was adopted internationally and it has remained the standard since then.
Some pitch standards have risen a little, particularly in Eastern European countries, in which pianos are often tuned to A444 or even a bit higher. Some concert halls in the UK and European countries have two pianos on site, one tuned to A440 and one tuned to A444. This satisfies the desires of performers and keeps the pianos stable.
That solved a few mysteries to me including the reason for having A444 on a tuner.