"A" is not a fixed point in nature. It's a reference pitch every orchestra agrees to tune around, and for most of musical history, nobody agreed on what it should be.
Pitch used to be chaos
Before standardization, concert pitch varied wildly by country, era, and even by orchestra — some 18th and 19th century ensembles tuned as high as 450–460 Hz, others well below 420 Hz. Instrument makers, choirs, and opera houses all had their own local convention, which made touring and instrument-sharing a genuine headache.
The push toward one number took decades. An 1859 French commission set a reference near 435 Hz (the "diapason normal"). In 1939, an international conference in London recommended 440 Hz as a shared standard, a recommendation that hardened into a formal specification — ISO 16 — in 1955. That's the actual, documented path to "440 Hz," and it stretches across more than a century and several countries.
The move to 440 Hz was a decades-long, multi-country standardization effort aimed at making orchestras compatible with each other — the same reason we standardize almost anything. It shows up in conference records and the ISO specification itself.
About the conspiracy theory
The version that circulates online is more dramatic: that 440 Hz was pushed specifically by Joseph Goebbels or the Nazi propaganda ministry because it has some subtly discordant, agitating effect on the human body, and that 432 Hz was suppressed as the "true," harmonious pitch. It's a compelling story. It's also not backed by the primary historical record — researchers and fact-checkers who've traced the claim have not found a credible source tying the 1939 London conference, or the later ISO standardization, to Nazi Germany specifically. Standardizing pitch was a widely discussed, multi-national goal at the time, championed by British and American standards bodies as much as anyone.
None of that means 432 Hz is meaningless — it just means the origin story usually attached to it doesn't hold up.
So is 432 Hz actually different to listen to?
Physically, the two are close: 432 Hz sits about 31.8 cents flat of 440 Hz — audible if you're trained and listening for it side by side, subtle otherwise. There's no published, controlled study showing that listeners reliably feel calmer, more focused, or otherwise measurably different with 432 Hz versus 440 Hz in a blinded comparison. What exists is a lot of anecdotal preference, and preference is real even without a mechanism behind it — plenty of people do consistently say they prefer how 432 Hz feels, the same way people have real, consistent preferences about warmer or cooler lighting without there being a health claim attached to it.
No blinded, controlled research has shown 432 Hz produces a measurable physiological or psychological effect that 440 Hz doesn't. Subjective preference for it is common and worth taking seriously as preference — just not as a validated health claim.
Worth knowing: plenty of musical traditions outside the modern Western orchestra never adopted 440 Hz at all — Indian classical music, for instance, is built around movable, relative tuning rather than a single fixed reference pitch. "Natural" tuning is a much bigger idea than one number.
Try it yourself
This is a case where the honest answer is: nobody can tell you what you'll hear. AUM includes both 432 Hz and the 440 Hz standard as one-tap presets specifically so you can A/B them on a song you know well, rather than taking either side's word for it.
Compare 432 Hz and 440 Hz yourself
Free on the App Store — one tap to switch tunings on whatever's already playing.