I have a piece of music written in C which I want to play on a midrange whistle. Im trying to decide whether to get an A or G. If I have figured it out correctly, with a G whistle I would start on E and would not have to half whole any notes. With an A whistle I would half whole or use alternate fingering on one note. Is this correct? I’m playing in a duo and don’t want to change keys. Also, any opinions on sound with an A versus a G whistle?
Hi Bairhands. Yes, that’s right. Playing in C on a G whistle is simple and you just use whatever you normally use for a C fingering (if you were playing a D whistle) to get the F natural. If you want to play in C don’t get an A whistle - it would be horrendous. Half-holing all over the place. 
There again, you could always use a C whistle …
You can play in C on a G whistle by using the xxx ooo note as your tonic (C) and playing the F using oxx ooo.
Oftentimes the range of a tune dictates that you use a whistle where the tonic is the “three finger note” xxx ooo rather than the “six finger note” xxx xxx, the nominal key of the whistle.
So yes for tunes in C I’ll often favour a G whistle, for tunes in D I’ll often use an A whistle.
The fingering oxx ooo takes away one sharp, or adds one flat, according to the key of the whistle. That’s what allows C on a G, D on an A, and so forth.
It’s also handy for playing tunes that drop a few notes below the tonic.
I’m always learning …but I always transpose the written music into the key of D or G then just pick the whistle you wish the music to come out in.
For example I was given a tune written in C to play in our band so I transposed it into D and played it on a C whistle …the key of C like the rest of the band.
This way you only have to learn one set of fingering …little or no half-holing.
…my head hurts 
John
Blimey! That seems like a complicated way of playing a piece of music in C … in C! 
In my choir days, it always seemed tunes in D stayed in the octave, while tunes in C wanted to drop down to that low F. I have a narrow range, down to a D, and I couldn’t sing those pesky C tunes in either octave. Tunes in G were the best either way.
These puzzles always confuse me!! Just as I think I’ve understood the theory, I lose it again. But surely if you transpose the music down to G, and play the tunes with normal D whistle fingering as if in the key of G (therefore no half-holes) then you’ll be playing in C. Yes? No?
What are you referring to Mike? If you transpose a piece in C to G, then play it on a C whistle with fingerings as if playing G on a D whistle, you’ll get the key of F, not C. It’s just a tone apart.
Or were you referring to something else?
Sorry, I realise now I didn’t make sense. Let me rephrase it. With regards to playing on a G whistle, surely if you transpose the music down to G, and play the tunes with normal D whistle fingering as if in the key of G (therefore no half-holes) then you’ll be playing in C. Yes? No?
Yes. Three-finger note sounds C on a G whistle.
I hear you …but it works for me! I only need to learn one set of fingering and transpose the sheet music up or down a few semi-tones accordingly to suit the whistles I have available.
Another example:- The piano in our band would be playing a tune in the key of Eb major so I transposed the sheet music up a few semi-tones to G major and played it on my Bb whistle …worked ok.
…my head hurts again
Am learning all the time …
Yes, that’s it. The only thing I still have a problem with is this:
To play C nat on a D whistle (and you need a C nat to play in G) you either have to half-hole or play with a forked fingering. So I’m still not totally sure what you meant, Mike.
[cross-posted - my post was in response to Mike’s and Peter’s posts above]
I guess part of my puzzlement is that it just strikes me as much simpler to play the tune by ear. Then you don’t have to worry about transposing at all. I can tell you, it takes a helluva lot less mental effort than all that mathematical stuff! (Though I have often had to do the mathematical stuff for other people - mainly classical bods who often seem to find the concept of ear playing alien.)
However, if it works for you, fair play to you!
play the tunes with normal D whistle fingering as if in the key of G (therefore no half-holes)
When I wrote this I was assuming a Cnat cross-fingering to be a normal part of the fingering repertoire, although obviously you can half-hole it too.