as far as singing goes,
every tune has a range

that range needs to match your range

which may mean either,
adjust the starting point ,
or don;t do that song..

lowering the key may not help either

fiddlers seem to like either c or d

the fiddle has a range too, at least
for players that use open strings

they don;t necessarily like playing in
a-flat just because you like it..

it may put them in unfamiliar positions,
using strings they are not used to,
or just playing in a range that
doesn;t complement the fiddle..

the open string thing is used a lot
in folk music styles, including
cajun

if you make them give that up, it starts
not sounding cajun any more

wle.

In standard tuning, you've got D, A, and G, all of which can give you on open string drone as a root or a fifth. C is a cool key, but the low open G can sound muddy, and the open is is a third. In Old Time, ir's a great key for tons of rags, If the fiddler is used to tuning down a whole step, that lets him play in C, G, and F, but using the positions of D, A, and G.
I know this is just opinion, but there's a resonance you get with those keys that's difficult (if not impossible) to achieve in a key with the double stops all fingered. I know people do it, but it doesn't sound 'right' to me.
I used to tell people I had a cheap fiddle, and it didn't come with any of the flat keys. Over time, I got used to it, but it really doesn't sound the same. One 'trick' I learned, playing with bagpipers. Their tuning is off standard just enough to make you pull your hair out. You can use a toothpick under the strings as a capo, adjusting it to match the bagpipes. Takes a little getting used to slightly altering your fingering postions, but it's a great time saver from having to retune for one or two songs.
Steve

If I get a G box, I'll have G and D for the fiddler to try to match. D would work well with a standard tuned fiddle, and since most of the songs I play on accordion are in second position, this could work.

If the fiddle is strung like a viola, CGDA, that could work. I have some extra fiddles I might try this with.

I tried singing one of the songs I have problems with, playing on my G/C box. I was playing the G row in second position, so it was D. I was wavering a bit, trying to find my spot, and it did sound a bit low, but I could hit all the high points no problem.

Since I've got a limited repetoire, "don't do that song" is not the best option for me.

The two songs that give me problems are "Blues de Voyage" and "Bernadette". They're wailers, which I like because it can keep me from sounding affected, but they do reach beyond my comfort level.

"Jai Passe" has a troublesome high in it too.

D...

Well most of what you're asking depends on who is playing fiddle. There are some fiddle players out there that can play with anything and it will sound pretty good. By pretty good I mean it will fit, but that's not to say it will sound entirely traditional. My personal favorite besides C and D to play with are A or E(with a standard tuned fiddle) but of the two I think most fiddlers would rather the A. B flat doesn't sound bad tuned standard but it's a little tricky fingering wise, hence why most fiddlers would tune down a whole step.

I think there needs to be a compromise between fiddle and accordion, but what it really boils down to is that if you're doing all the singing, they better learn to play with what you're using or learn to sing quick. But then again, I like a good challenge every now and then

John

Our fiddleplayer use two fiddles.
One is "standard" tuned and he plays it besides the D-accordion. The other fiddle is tuned lower and this one he plays with the C-accordion.
I know that in the old days there was a problem between fiddle and accordion players. The accordion and the fiddle didn't sound good in that days.
Who was the first fiddleplayer who tuned the fiddle lower ?

Bob.

I knew there was something about Bob!

I know a lot of Old Time fiddlers tuned to what sounded good to them, without a tuning fork or any other aid. Many played with banjos that couldn't be brought up to concert pitch, so the instruments were tuned relative to each other. I'd bet there were some fiddlers that just went ahead and tuned to the accordion, not thinking in terms of tuning down. In this age of tuners in every instrument case, going to a festival with lots of jams, you can pretty much count on everybody being in concert pitch. A few years ago, bouncing from one jam to another meant retuning to some degree was a given.
Steve

I guess I've answered my own question somewhat.

If the original song I play is in G on a C box, I could then get a G box, play it in D, and the fiddler should have little problem playing on a standard tuned fiddle. The strings primarily played will be the middle two, rather than the upper two. To me that would not be a problem, because I don't go all over the fingerboard when I play. To some it might limit their playing.