@voltronic hmmm, had to slow this one down a bit for my level. And I was surprised by one of the very first points: as a kid, I remember asking if a C# and a Db were the same, and I was told there was a 1 coma difference, a sharp/flat changing the note by 5 commas (out of 9 for a full step). I was also told that (non-fretted) string instruments players, for one, would play a C# differently than a Db. Is any of this true?

@sgalzin
First of all, I'm extremely impressed that you learned any of that as a kid. Understanding commas in tuning systems is a pretty advanced concept, and I don't think any of my post-Masters work covered it. I just sought it out on my own because I love theory.

Secondly, yes, that's true too a small extent today, but not as much as it was a few hundred years ago, and not if playing alongside instruments with very fixed tuning (piano, mallets, fretted strings, etc).

@voltronic well I was mainly geeky / mathy, I guess :) But back to your point, that implies that a string quartet might pay attention to that... My cousin is in a string quartet, I'll ask him for an example maybe... will share if I get a good example, though I'm not sure my ears will be good enough to tell the difference :) thanks for the answer! (and yes you are right, a comma, not a coma :) )

@sgalzin
Too much discussion on this topic might run the risk of putting some people into the latter state. 😑

@sgalzin
It all connects to the concept of "temperament" and the different types of commas figure heavily into it.

Choirs can also mess around with different temperaments, but it takes a lot of skill and very attuned listening.

I'm no expert on this specific area, but this seems to lay out what you need to understand it:
https://www.britannica.com/art/tuning-and-temperament

@voltronic well this page was super interesting (it also answers the question from the practical POV of a string ensemble, saying there is no evidence that players use the 'just' temperament). I added a bit of wikipedia to that and now feel better equipped. And I think the 9-comma thing I was told is wrong. Thanks for all this!