People tend to be more bothered by the sharpness of the C nat than of the flatness…even if the C nat is perfectly in tune, people still prefer it to be a bit flat.
However, and maybe I’ve had too much coffee this morning so with no intended slight of the OP, I must wonder why there is so much focus on Cnat?
It seems to me that we focus far too much time and energy on Cnat. I also wonder why there is not equally as much attention focused on low E since it’s consistently the weakest note on many, if not most, whistles? Of course we’re talking about D whistles or the relative equivalent position.
Whistles that do not offer a consistently achievable cross-fingered Cnat work well by half-holing L1, which does take some practice, but is not difficult, and ALWAYS works. Half holing is the ONLY way to achieve certain notes (Fnat has NO other consistently usable option) so one will need to learn it anyway. However, there is nothing that can be done to strengthen a weak low E and it is far more prevalent than the Cnat issue.
One could argue C natural (or should we say the flattened 7th?) is a very important and expressive note when playing Irish Music. It IS a note to fuss over (and I say that as a piper first and foremost).
When I said, there are several ‘in tune’ C naturals and I was
Of course we all know the OP, erroneously, meant the equal tempered Cnat as the ‘in tune’ C natural.
Considering a just intoned C natural: it is the fourth above the G, which in turn is the fourth above the D. The fourth is about 2 cents flat of ET, so there is not much difference to ET tuning. What other intervals are making a difference for the C nat?
Personally I just like it right. Sweet to the G, as it is part of G major and associated modes.
On the pipes a C nat 29-ish cent flat of ET would be one of the Cs to use. I agree you will want it right but then again, there’s more than one ‘right’ depending on the situation so flexibility of intonation is probably a more important factor for both instrument and player.
I guess some people find it a more “issued” note because it is the most fingered variated note so to speak…and people with musical hearing can sometimes be bothered by the different frequency they get on a different whistle using the same fingering they use on their own whistle.
The thing with tin whistles is that the note is also affected by the players breath pressure and so to say “rhythm” of playing the octave…3 players can play the same whistle and get different micro results…
Another option is that people use more air on that note (which cause the sound to get a bit more sharp)…