Fundamental pitch is determined primarily by the length of the source of the wave-form, whether the waveform in a breath instrument determined by the tube the air travels in (roughly speaking… the pressurized air actually extends out a little bit in certain cases); anyway, lay a D flute next to a Low-D whistle and you will find that they are the same length, hence the same fundamental pitch.
I have been told that this fundamental pitch is the D above middle C, but I’ve not taken apart a piano to measure the string at middle C and my digital tuner does not declare octave, so, whatever.
The high-D whistle, however, is remarkably shorter than the low-D whistle, by about half, which doubles the frequency of the waveforms within, which puts it up more or less exactly an octave.
So, the only way that the D-flute and the high-D-whistle are the same is if the D-flute is normally played in the first and second set of overtones rather than in the fundamental tones and first set of overtones… I think any experimentation at all, checking with any maker, etc., will quickly reveal that this is not the case.
Therefore, a high-D whistle plays one octave higher than a flute or a low-D whistle.
Now, whether a high-D whistle plays D-above-middle-C or D-above-C-above-middle-C is really irrelevant. If it plays D-above-middle-C then flutes play D-below-middle-C, if it plays D-above-C-above-middle-C (which I believe is the case) then flutes play D-above middle-C.
Some confusion comes from the fact that we essentially treat whistles as one-octave transposing instruments, that is, we read music as if we could play from D above middle C and up two octaves, effectively transposing all music up an octave. (The other choice being to not play notes in the first octave, play notes in the second octave in the whistle’s first octave, etc., which is what classical musicians do… but they have other instruments filling the gaps…)
So, we -say- that the whistle runs from D above middle C and up two octaves, because that’s how we read music for it, but in absolute pitch, it’s an octave up.
Or, possibly, but I don’t think so, every other irish instrument is an octave low (mandolin, flute, low whistle, fiddle, uillean pipes, … )
Which brings me back around to wondering whether the concertina differs in pitch from the button accordian, but I guess I’ve inferred that the answer is dependent on the reeds in it, but that answer makes me wonder what kind of musical principles they work on. Anyone have a broken buttonbox I can dissect? 
–Chris
EditPS: The idea of playing in the first two sets of overtones, btw, is not absurd. The Bb military-style fife is played this way, and has in-tune first and second overtones with the fundamentals weak and out of tune, as opposed to flutes and whistles which have in-tune fundamentals and first set of overtones…
[ This Message was edited by: ChrisA on 2002-05-10 18:03 ]