Here is a lengthy discussion about accordion tuning from the discussion group
Here is from a web site of a French maker of SERAFINI Accordeons
Here he demonstrates the different amounts of variation with a two row Hohner Pokerwork.
This is about "DEDIC" tuning as compared to standard tuning of two reeds.
In simple terms.. instead of tuning one reed to standard pitch such as an "A" to 440 and the other higher.. you tune that "A" reed lower and the other the same distance as you would have for the other.. see below.
"Here's an example of an octave interval between the notes A4 and A5 using, say, a 4 Hz tremolo:
A4 Reed 1 = 440 Hz, Reed 2 = 444 Hz, Perceived pitch = 442 Hz
A5 Reed 1 = 880 Hz, Reed 2 = 884 Hz, Perceived pitch = 882 Hz (i.e. somewhat flat of the true octave frequency of 884 Hz)
Therefore when the two notes are sounded together e.g. in a RH chord, it will sound 'rough' because the interval is not a true octave.
However, in Dedic tuning:
A4 Reed 1 = 438 Hz, Reed 2 = 442 Hz. Perceived pitch = 440 Hz
A5 Reed 1 = 878 Hz, Reed 2 = 882 Hz Perceived pitch = 880 Hz
This time the perceived pitches of the octave interval is exactly double the frequency and so it will sound sweet and in tune.
You can extend these calculations to all other intervals, not just octaves, but they're the easiest to illustrate the principle.
The other advantage of Dedic tuning lies in the LH bass notes and chords. Because these are not tuned with a tremolo, but should be 'spot-on', the bass notes will always sound in tune with the RH notes.
E.g. a LH bass A fundamental with three reeds tuned at 110 Hz, 220 Hz and 440 Hz will always sound in tune with a Dedic-tuned RH side, in this example the perceived pitches of the RH side A notes will be 220, 440, 880, 1760 Hz, etc. - always doubling the frequency and always a double multiple of the LH side. In a non-Dedic tuned instrument, there will be increasing discrepancy between the LH and RH sides as you go higher in pitch.
Hope this explains the basic principle of Dedic tuning and why it is indeed different from standard tuning. "
Dedic is good if you are playing all the reeds all the time.. meaning both middle reeds together all the time.
But if you want to play just one of the 2 middle reeds.. neither will be in tune with other musicians.. One reed would be higher or the other reed lower and may clash with every one else such as the fiddler or guitarist.
DEDIC tuning is common in Quebec.. or was.. my first custom made Quebec box from Clement Breton was DEDIC tuned... when I sold it the Irish buyer had it tuned standard.
Most manufacturers do not tune to the DEDIC formula.. you would have to go to a tuner familiar with the technique.
In England DEDIC tuning is becoming popular on two row boxes in the favored Brit key system of D/G
Jim Pettijohn discusses his project of "progressive tuning" back in August - September 2012.
Most Euro made accordeons are "progressive" tuned , they just don't call it that.. they call it tuning.
Tuning is a very dark science, and with one row accordions, it's really a matter of what version of out of tune do you like best. We've mostly simplified it in Cajun music to a somewhat standard style, at least when dry. The one debatable topic is whether to sharpen the 4ths or not. Some do, some don't. I didn't used to, now I sharpen the 4ths about 10 cents to start.
The one area I'd like to experiment with is what Jeff is calling dedic tuning. I've done one that way. I'm not a fan of wet tuning for cajun music, but I'd like to experiment more with this. Experimenting with tuning is not very appealing in the manner that you have to remove metal each time you tune a reed, well, that and the fact that I'm getting lazy in my old age.
So, in a nutshell, DEDIC is LM+M-H as is common on Quebec boxes?
"So, in a nutshell, DEDIC is LM+M-H as is common on Quebec boxes?"
Usually designated as L M- M+ H
It used to be more popular. As of late in Quebec one M row at "A" 440 then the M+ row.
If you see a description "equal tempered tuning" usually means no dedic.
I have a Quebec made box on its way.. when it gets here I'll see if it's dedic. About 10 days.
Consider this.. With dedic tuning if you want to play with only one M reed you are out of tune with every one else.
Often you will see Quebec boxes with non functional stops or only the L and H have working stops or no stops at all.. or often 2 reed boxes with fixed or no stops. These could be dedic as the idea is that MM are working all the time.
If you close off either of the M reeds you are out of tune with every one and yourself.