Hmmm. Now I'm even more confused Geoff. Isn't the "reference zero" note you mention the same thing as the "center point, key or note"?
Not necessarily Jody. Let me try to explain:
The centre point (or Key) I use on the EC is C. this equispaces the useable keys like this ; AB,Eb,Bb,F,( C ),G,D,A,E , so we have four Keys sharp and four Keys flat of C.
The 'Reference Zero' note is in regard to the Diapason. So, one might use A as Zero, as in 440hz but A is, in a Key sense, not so close to C. So one could choose a different Zero in reference to Standard Pitch. I have used both G and D for this but look what happens:
Note deviations from Equal Temperament with A as Zero ( for 1/5th Comma Meantone).
C= +6 , C# = -8 , D = +2 , D# = -12 , Eb = +12 , E = -2 , F= +8 , F# = -6 , G= +4 , G#= -10 , Ab= +14, A= 0, Bb= +10, B= -4.
With D as Zero; take 2 cents off each of the above. ( meaning to use D as on a Tuner set to Standard Pitch)
For C as Zero subtract 6 cents from each of the above. Etc. Etc. Of course this will make the whole instrument flatter.
This moving of the reference Zero can be used to place the notes in the best possible position for playing with certain instruments that are not tuned to Equal Temperament.
Changing the Key Centre note is usefull if your range of keys is spread more to one side or the other... so on an Ab/Eb anglo it might be better to use Eb as the centre Key and chose a zero note that did not make the concertina too flat or sharp overall in comparison to the International Pitch standard.
It might be worth a listen to some more recordings I made for the Tune of the month forum... you can find these on Soundcloud.com by searching 'Geoff Wooff'. They are not wonderfull recordings but the one called STE-007 is interesting for this topic because I played the tune in seven different keys in one take. The other 1/5 Comma recordings are Valencia Harbour and STE-031.
My reason for using a Meantone temperament on the EC is because the Major thirds are a very easy and usefull harmony , on this keyboard, which sound so horrible in ET especially on a metal ended model. This way I am not restricted by the need to invert chords or otherwise re-arrange harmonies.
Edited by Geoff Wooff, 07 June 2016 - 06:48 AM.