A440, explained — and what 432 Hz actually is.

Through the 19th century, European orchestras kept creeping upward. A brighter, more brilliant sound was fashionable, and there was no authority to hold the line — so concert A crept sharp, venue by venue and decade by decade. Across cities and eras it wandered somewhere in the low 420s to the 450s: there was no single “concert pitch”, just whatever the local hall and its instruments had settled on.

Singers paid for it. As the reference pitch rose, every written note sat a little higher than the composer had heard it, and voices were pushed nearer their limits. The pressure to standardise came, in no small part, from the throats of the people asked to sing sharper each season.

France acted first. In 1859 it legislated the diapason normal — a legal standard fixing concert A at 435 Hz. It was the first time a government had written a pitch into law, an attempt to stop the drift by decree rather than fashion. 435 became a widely adopted reference across Europe for the rest of the century.

An international conference in London in 1939 settled on A = 440 Hz. The International Organization for Standardization later codified that figure as ISO 16 in 1955. That single number is the anchor for this entire site: fix A4 at 440, and every other note follows from the formula f = 440 × 2^((m − 69) / 12).

Modern advocates attribute ancient or healing significance to 432 Hz. There is no acoustic or historical evidence for this. The number is simply about 31.8 cents flat of 440 — worked out directly as 1200 × log₂(440 / 432) ≈ 31.8 cents. A semitone is 100 cents, so ~32 cents is a small, real interval: enough to hear as “slightly lower” in a direct comparison, and no more mysterious than that.

The Verdi connection is a modern retelling. Verdi did campaign to lower pitch in Italy — toward the lower French standard, to spare singers — but the specific 432 attribution is contested and doesn't come cleanly from him. The honest line is the simplest one: 432 sounds different because it is different. Tune your A about 32 cents down and everything shifts with it — that audible warmth is the whole phenomenon, ratio and nothing else.

440 Hz is the standard, and it's what your tuner, your DAW and this site assume. But the old habit hasn't vanished entirely: several major European orchestras still tune slightly sharp, commonly around 442–443 Hz, for a brighter sound. That's why every note here carries a small variant table — see A4 at 432, 440, 442 and 443 Hz — because “the frequency of a note” only means something once you say which A you tuned to.

For two centuries before electronics, pitch travelled in a pocket. The tuning fork was invented in 1711 by John Shore, a trumpeter and lutenist at the English court — a small forked bar that rings at one fixed frequency when struck, a portable reference you could carry from hall to hall. It is why this site's mark is a tuning fork.