I’m fairly new at this, so please excuse an elementary question: what is with whistles in all 12 keys? I can understand the need for other keys if you are performing, since you would need to accomodate vocal ranges, other instruments, and tunes that are not traditionally Irish. But if I am solely interested in playing in sessions, do I really need anything more than my trusty high D whistle? After looking at some lists of popular session tunes, it appears that less than 5% are in keys that aren’t natural to the D whistle.
Hi Obie, welcome.
Yes, you’re basically right. A D whistle handles most typical Irish trad session repertoire you’ll encounter. Add a C whistle, and you’ll cover nearly all the rest. And for any keys you can’t handle, it’s perfectly OK to sit there and simply enjoy what the others are playing. 
I agree, one D is all you need.
Unless the session gets so rowdy that your whistle is in danger of being severely damaged 
. Then a backup is not a bad idea.
I agree that D and C are really going to cover most of what is out there. I hit sessions every now and again that have a preponderance of fiddle players and they tend to dominate many of the sets that are played. As such I find some good mileage in an A whistle. This will allow you to play in D (as you would in G on a D whistle) with an extended bottom range and a really strong low D as it is rather in the middle of the whistle. I use a Medium bore susato for the job… Just a thought.
12-13 years at sessions and only played a D whistle (well, I mainly play flute, but I do play whistle and only a high D…the flute FWIW is the standard concert/low D flute, and I’ve never felt a need for one in another key, either)…you can half hole anything, easily, on a thin walled trad (e.g., generation/feadog) style whistle. I’ve never seen the need for another key if you can play chromatically on a D whistle.
Just my $02.
Eric
After the D and C keys, I find the next most useful is A. Sometimes the fiddles like to play in A. But that’s also a good time to go get a drink.
I third the opinion on ‘A’ as a good key. Just bought one, and at the session i attended last week i used the A whistle the most actually.
Hey, anytime is a good time for that! But you really should be able to play AMaj (and AMaj family) tunes on your D whistle. All you need is a good G# cross-fingering in the 2nd octave, usually either xxoxxo or xxoxox. In the 1st octave you can either fudge it with xxoxxx or half-hole it. I always consider AMaj to be one of the “native” whistle fingerings.
If you want to be lazy for AMaj tunes, an E whistle is usually a better choice. The G fingering gives you a better range for the common gamut of A tunes. With an A whistle you often find yourself stuck in the wrong octave with quite a bit of octave folding. Not that A whistle can’t be a change of pace for tackling AMaj and DMaj tunes. But I’d consider it 4th choice behind D/C/E in a session kit.
For sure, but I probably use the A more for D tunes with lower notes and poor foldability…
With an A whistle you often find yourself stuck in the wrong octave with quite a bit of octave folding.
So could also say this of the D whistle.
Since the OP referenced Irish tunes and sessions, I’d say actually not.
The most commonly played Irish session tunes don’t drop below D, and fit perfectly on the D whistle in range, not to mention D flute and pipes. These melody instruments often dominate a session.
For less common fiddly tunes that may drop to the G string, there will be well-worn and well-known settings that D whistle, flute and pipes play, and which are in effect the real windy settings of the tune for those instruments. You just learn them like any other tune. You’re not stuck in the wrong octave if everyone’s playing the same thing as you. Add the fact that octaves are quite fungible in practice on winds anyway (especially flute), and the objection mostly vanishes.
In any case, I don’t think we want to give the OP the impression that an A whistle is essential Irish session kit. I almost never see anything but D/C whistles at sessions, including in my own hands.
I am with MTGuru in feeling you do not need a lot of whistles in an ITM session…D whistles or flutes only for me.
Eric
MTGuru/Jayhawk: useful was/is the word, not essential 
I’ll grant you at least use_able_.
I guess that’s what i can twist out of you so i’ll settle for that ;-p
even though i find it useful to be heard in a large session, playing what corresponds to the three lowest notes on a D-whistle
Don’t get me wrong, I’m not saying that anyone shouldn’t buy a whistle in a different key, but in just the last 10 years of sessions I can only recall once where a whistle player brought out a whistle in a different key. Everyone else just uses a D whistle (high or low). Granted, my sample size may not be huge, but I’m including sessions in Sacramento, Davis CA, San Diego, Seattle, St. Louis, KC, Baltimore, and Atlanta (that I can recall).
Now in our band we have a couple of players who break out different key whistle from time to time, but at session they just play a D whistle…or the bodhran. 
Eric
No worries, i am not saying the opposite either 
It’s just that in my ‘circles’ if you want to play along to the odd song now and again you’d better have whistles in other keys than D or C, namely A, Bb or F (low F is handy in those cases)
Ah, you have jogged my memory…we don’t have much singing in our session, but there have been a few other times, during a song, when a whistle in a different key came out of hiding to harmonize with the singer.