I became interested in the whistle a number of years ago (including following C&F). But this year I decided to begin a serious effort to learn to play the instrument well. Of course I have acquired several whistles–5 in D, 2 in C, and one in Bb. As I practice either tunes or exercises, I find that, if I stay in the second octave for awhile, going back down, especially to D, E, or F#, is difficult. The notes don’t want to sound. It doesn’t seem to matter which whistle I am playing, either.
I’m an old French horn player and had a similar experience transitioning through the ranges on the horn. That was a matter of adjusting the embouchure. But playing the whistle does not involve manipulating an embouchure. So I’m not sure what else I can adjust to get a smooth change of register with good sound. Any advice from this august group would be greatly appreciated.