440 is the international standard as of around the 18th century iirc. Before that it varies a bit from 430-450hz depending on region and time period. 432 is mos

440 is the international standard as of around the 18th century iirc. Before that it varies a bit from 430-450hz depending on region and time period. 432 is mostly about preference although its origins go back to setting c as perfect integers. With this tuning c4 is 256hz, c5 512hz, etc whereas at a4=440 c4 is 261.63hz. https://roelsworld.eu/432-tuning/the-scale-of-fifths/ https://roelsworld.eu/432-tuning/the-scale-of-fifths/ this goes far more in depth It’s ultimately just preference though. To that end some symphonies use other options, ny philharmonic uses 442, Boston symphony 441, etc. When I marched and teched drum corp we did 442 because that’s what the marimbas were tuned to plus we performed outside in the cold so going up a touch helped as the cold would generally pull everything flat.