Music Tuned to 440 Hz versus 432 Hz and Health Effects (2019)

Hard agree. Worked for an instrument builder for a decade, of fixed-pitch esoteric instruments. Client community had a distinct minority who went all in on such things as 432 Hz woo-woo.

Happy to make them, with the footnote that instruments made to this or other custom-request references could not play in concert with most others.

No discernible difference, with one interesting qualifier: for acoustic (or emulated) instruments one is familiar with, there is an audible shift in timbre correlated with tuning to different resonances, most dramatically if you retune a given specific instrument.

This is because you are shifting the fundamentals and overtones of the instrument while keeping the natural resonances of the instrument fixed. This naturally produces a different "signature" of relationships between such frequencies and in the case of the instruments I was close to, in their internal resonance, which was completely defining of their "character."

(Something similar is going on with pitch-shifting algorithms which do "formant correction" to try to keep voices sounding natural within modest shift of pitch... we have deeply internalized expectations wrt the various resonant landmarks in human voices because of the bounded variation in their geometry and the physics of voice production; this is less so but absolutely still true of familiar acoustic instruments.)

One of the similarly anecdotal but significant "tells" of the placebo nature of perceived difference in 432 Hz and 440 Hz is to my memory, very few players were incapable of telling instrument key, let alone pitch referent, based on hearing them alone. (Knowledge of available instrument keys and tunings was commonly deep given the cult following they received.)

There's a whole genre of music called Slowed and Reverbed that slows all kinds of music down. Here's an example of a slowed song and a it's original:

Cigarettes After Sex - Slowed https://youtu.be/GGfWuK-fZYM

Cigarettes After Sex - Original https://youtu.be/sElE_BfQ67s

You're not wrong that you wouldn't be able to tell the difference as long as you don't have perfect pitch (it's a fraction of a semitone), but you might want to check your math.

There seem to be other things the article doesn't tell us, such as how the authors verified that the music they used had been tuned to A=440 in the first place (since it's far from universal) or why, given an infinite number of possible tuning frequencies, a great many of which have been chosen by musicians at some point, and given no obvious physical basis for this specific choice, they went for A=432 instead of any other value below 440.

[edit: removed warranted but uncivil snark]

A 432 A makes the math behind music so much nicer to work with (ignoring legacy baggage).