Key signatures for modal tunes
Is there a ‘correct’ key signature for modal tunes?
As part of my "tunes I really should know by now" program I’ve been learning An Phis Fliuch, which given that it has a single sharp but resolves on D (it sounds modal to me, anyway) I am deducing is in Dmix.
Flicking through a tune book the other day I came across it written with two sharps in the key signature but all the C’s naturalised. Musing over this on one of my many long distance car journeys, I came to the conclusion that this would be the ‘right’ way to annotate the tune. It doesn’t make any difference to us melody players, but points the backers at D as the tonic, not G. I notice that the version of the tune in the database here is listed as G major, but someone has pointed out in the comments that it is actually Dmix.
Apologies if this has been covered before - I did a search but didn’t find it.