Brand-spanking newbee, so if this sounds stupid, cut me some slack. Oh, and I can’t read music for squat. 
Just for grins, I’d like to try and play “Ripple” by the Grateful Dead. The first note is a “B”…two down from “D”.
How in the world would you finger that note?
Ummm… L1 (i.e. XOOOOO)
Pat
Hi VAC, welcome to Chiff & Fipple, and the exciting world of whistles. 
Pat,
No, that B is too high…I need the B on the next octave down (if it’s even possible).
Patrick
Nope, not possible. You have to a) Play any notes below low D up an octave; or b) Transpose the song to a different key; or c) Use a whistle in a different key.
That’s the answer I was afraid of! 
Thanks for y’alls help!
Hi VA - welcome to the exclusive ultra-norm-neuveaux werld of whistledom 
hmmm .. Ripple is essentially in G. That can be played on a D whistle, but on a normal high D it will come out shriekingly high .. perhapse it will have its charm if played with confidence Otherwise, you can use a low D whistle or an alto G whistle.
Your notes will be a selection of: G A B C D E and F#
So on a low D - that’s all the normal notes except C - which is played OXX OOO in the first octave or OXO OOO in the second octave (or D00 000 with the top hole half covered).
On a G whistle it’s all the normal notes. You would start on XXX XOO.
Great song. I hope you get it down!
Thanks, Mitch.
I usually cough when there’s a note I can’t play…
Yes if the lowest note in the tune is B and the tune is in G major it might work best on a Low G whistle.
But it’s very common for trad Irish tunes in G to have a Low B or two, and these tunes are nearly always played on a D whistle. Just those Low B’s are played an octave up, the rest of the tune stays in the usual octave.
A common example is the reel The Banshee which starts
GGGD EDBD | GGGB d_Bd | etc
The B in the first bar is played low on accordion, fiddle, tenor banjo, etc but high on flute, whistle, and uilleann pipes. Nobody even notices.