I don’t know anything about music theory, but this question has been nagging on me for a while now…
Why is the F note sharp? I can understand making the highest note C# - you can still work down to a C nat, but you couldn’t work up to a C#. But why is the regular F note not F nat?
Mike
It is worth knowing, even a bit, how scales and modes are constructed.
Look for what is said shout the major scale in D, somewhere down that page where modes in Irish music are discussed.
Sorry if you already know this
If you are starting on a D and you sing “doe, a deer” from The Sound of Music, “Mi” will be F#. Why? It “sounds right” especially to the ears of Euro-Americans. I mean if you sing that song and start on a D you will sing an F#. Everybody will, to the degree that they are able to actually sing in pitch. Why it sounds right is a more complicated story–is it familiarity and training, or some kind of natural pattern? Long story.
If you start “Do, a deer” on a C, “MI” will be an “E”. If you start on a C#, “Mi” will be an “F”
The most common key for a whistle is D, and so you have F# on a D whistle. Otherwise you would not be able to easily play most tunes in D.
On your profile you mention not wanting to annoy the family when you practice. One way to do this is to get a Bb whistle, much less shrill. But then it’s harder to learn by ear
You can get some wonderful holiday photographs of the key of D here:
https://www.basicmusictheory.com/d-major-scale
F sharp comes in very handy in other situations. It’s the leading note of G major, and G is the fifth semitone higher than D, and key of D whistles play the key of G fairly easily. Key of A whistles play the key of D very well and F# is the 6th note of A major. F# is the fifth note in the key of B, which doesn’t sell, so on the black market F# is sometimes repackaged and sold at a discount as Gb to C# addicts.
Your Honor, I object!
It depends on the person. Me, I’m almost exclusively a by-ear learner, and transposing is no problem. It doesn’t make me better or anything; it’s just how it works for me. The really important thing, I think, is to have the tune rock-solid in your head first and foremost; I’m less convinced of the advantages of playing along when learning. Besides, the fingering is going to be the same no matter what pitch whistle you play the tune on, so if you’ve memorized it, nothing can stop you.
No I mean it’s harder because you have a Bb whistle and the tube you are trying to learn is probably in D
Same difference. Let me try to explain myself from a different angle: Forget your instrument. Simply learn the tune by ear, which means by listening, not playing. You should be able to hum or lilt it all from memory, and then you work it out on the whistle; the key is immaterial, for it has nothing to do with the structure of the tune. That’s the essence of the process. Very streamlined.
We’re so darned lucky to be able to even have recordings at our fingertips these days, that finding good examples can be the main challenge. But the more experienced you get, you can grab a tune even from a characterless, stiff MIDI and make it into something better.
How about that F#, eh? 
A whistle in the key of D has 2 sharps, F# & C#, this comes about because of how scales in each key are made, they are a combination of whole tones & half tones.
Tones = W - W - H - W - W - W - H
Notes of key of C = C - D - E - F - G - A - B - C
Notes of key of D = D - E - F# - G - A - B - C# - D
Etc.
I’m with Nano. Unless it’s Beethoven, when I know a tune, I’ll play it on whatever key of whistle comes to hand (or any other instrument I can pick out a scale on).
Correction: Even Beethoven. I just played the Ode to Joy theme in Eb on a Bb whistle. Purists are cringing.
And I’ll bet it was with what we call “G fingering”, too. I hope you washed your hands after that.
But to the point, Tunborough: Had you ever played the theme before?
I get what you guys are saying. And for a very experienced player is very doable. But for new players theres several issues.
If someone hears a song and is trying to figure it out, it might not be in the same key as their whistle (or in the G fingering key). Beginners especially, cant hear a song, and then be like “oh if I just think of it a half step down thats will be in Bb and I can play it on my Bb whistle”, and then be able to figure it out. Its significantly easier to think of a song or listen to it, and ear it out, when you already have the right key whistle. I just had this issue the other day. I was trying to figure out a song with no success, because I wasn’t sure what key it was in. The second I figured out what key it was in I picked up the right whistle and figured out the melody in seconds. This was not a complicated song, and I know the melody by heart. But because I was trying to play to a song in a specific key, until I have the right whistle key its much harder.
My brother told me it was in G so I was trying to play it on a G whistle. He left out the part where it’s actually in Gm, so I needed a low F. So I could get part of it right on the G and then realize I cant play a few of the notes. I was trying to start on thefirst note which both whistles have. But obviously the G was missing notes it needed.
If someone is trying to figure out a song with no track, it can be in whatever key they want / are thinking. But then they still need to find the right key note to start on (if that wording makes any sense). In the above I knew what the first melody note was, and it was on both whistles. So if in a players head, they think the first note is a C, and try to play it on a G whistle, they are going to run into problems quickly. They need to know that the key they are thinking of it in needs to be played on a low F. More advanced players seem to be one with keys and scales and can figure out what key its in, or what part of the scale the melody starts in, which would translate to playing it on any whistle. I’ve improved in this department but am not there yet.
My brother told me it was in G so I was trying to play it on a G whistle. He left out the part where it’s actually in Gm, so I needed a low F. So I could get part of it right on the G and then realize I cant play a few of the notes. I was trying to start on thefirst note which both whistles have. But obviously the G was missing notes it needed.
You could even have tried a C whistle
Which opens the other can of worms that makes whistle keys so painful for new players. You can Play in F on a C, and in Bb on an F, but you cant play in Bb on a C because you will be missing 1 note. And you can play in C on a G but you definitely cant play in F on a G (Excluding half holing and weird fingerings). Which starts opening a lot of doors for picking up the wrong key whistle and still being able to play the tune in the key you are thinking, but then getting to another part of the tune and realizing you’re missing a note, and need to completely change your fingering and whistle key to be able to play it correctly.
Don’t forget that seasoned players were once beginners, too. Everybody’s different, so don’t think your experience is what all beginners experience. We don’t.
I never had that issue so I don’t know how to address it, other than to suggest that maybe you should do the harder thing on purpose, as an exercise. And that means fiddling around until you get it. It works that way for me, too, the only difference being that I’ve had more time at it and have gotten some things out of the way. Your chops can only improve if you do that.
But here’s a sort of reverse-engineering, if you will, to that: Play the tune in the key you work best in, and pay attention to how your fingerings sit. Do the exact same thing on a different key whistle (IOW, as if it were the previous whistle), and there you go.
See, there you go listening to your brother and getting hung up on keys. He didn’t even give you the right info, so you should drop the concept altogether except when needed to play with others. What key is Happy Birthday in? How about Twinkle, Twinkle Little Star? Depends, doesn’t it. I’ll bet if you hummed them one day you’d hum them at a different pitch on another. I know you know those tunes rock-solid - we all do - and I’ll bet you could pick them out on any whistle of any key. Might not be as fast as you’d like, but I’ll bet you could do it. That’s what I’m saying here.
Sure it does. Everybody has to find the starting note when it comes to new tunes. With exposure and practice, it gets easier.
And why would you try to play in Bb on a C whistle? These aren’t pianos; all you basically get are seven notes (well, eight if you count the natural seventh), seven modes, and two octaves - so if you want to play in Bb, you prepare accordingly with the appropriate whistle. Either that, or you become a half-holing wizard.
It’s why so many of us have whistle collections of numerous keys and pitches.
You can Play in F on a C, and in Bb on an F, but you cant play in Bb on a C because you will be missing 1 note. And you can play in C on a G but you definitely cant play in F on a G (
Which reminds me of a number of occasions when playing tunes with a neighbour. I was playing the D Sindt and she was playing hers. After a few tunes she took out her C whistle and played along on that for the rest of the time. That happened on several, separate, occasions. I didn’t question it but I assumed it was because we were playing in a noisy-ish public spaces where it can be very hard to hear what you are playing and what the other is playing when two whistles of the same sound are going together and blending into one. Changing to a whistle with a slightly different tone can alleviate that problem, even if it means transposing the fingerings a tone up. Whatever the way, it was no bother on her. 
Make of that what you will.
Yeah, I’m too lazy for that.
But I did play a C whistle next to a D whistle once just to be aggravating. The dissonance nearly made my head explode.
We’ll yes, so am I but it does show some people don’t see limitations.
I can recall several occasions where flat sets were played and someone wanted to join. ‘We are playing in C’ the usual warning. ‘No bother’, the reply and often it wasn’t. Concertina or fluteplayers not missing a beat after joining. A mandolin player too once. Some people are very clever like that. I suppose it’s in being unfazed by transposition, knowing your instrument and your tunes and just doing it. Mind you, on occasion it was a problem and people had to be told and there was one who played along in D for a whole set of tunes without noticing we were in a different key but then, there’s always one.
Yes it was “G fingering”, with “C-nat” (Ab).
Yes, I confess I’ve played it many times.
If you start on a C#, Mi will be an E#. The distinction’s actually quite important when you list the whole scale:
C# D# E# F# G# A# B# C#
Or:
Db Eb F Gb Ab Bb C Db
Rather than, for instance:
C# D# F F# G# A# C C#
Where you have duplicate letter names and an illogical ‘scale’.
Up to today I hadn’t at all, so I thought I’d give it a try. The point here is that I’ve already got the melody to memory - indeed, I think most of us do - so the task is to find where it sits on a whistle. A rank beginner would probably be more likely to go with trial and error, but they can definitely get there. I know this for a fact, because I’ve been there, and the notes are waiting faithfully for us to find them. After having some years under my belt, it gets easier: Rather than the prescribed Eb, let’s take a D perspective (which I usually come from, not being so swift with the theory stuff); since it’s a major diatonic melody, experience tells me that on a D whistle, the tonic’s going to be D or G. D’s great, but - drat - it doesn’t go low enough, which leaves me with G. And G does the job perfectly. And like Narzog, I too had to find, with my fingers, where the tune’s first note sits, because it’s not G, and I’m no genius. But that done, you’re off to the races. The fingering’s the same no matter what key whistle I play it on. The structure of the tune is what gets carried over from key to key, regardless. Taken that way, it doesn’t have to be in Eb.
Sorry to distract from the original F# question, to which this is only tangentially related.