You’ve all been great at answering my questions- and I have another one. I have a Dixon brass high D- it seems to me that it is hard to get as much sound out of it when I play the lower D on it in particular, and a bit like that for the lower E as well. If I push it at all, it will jump to the next octave on those notes so I have to hold back on those unlike the other notes. Is this something I am doing wrong? Something particular to this make/model of whistle? Or??
What you’re describing is a characteristic of most whistles to a degree. The Dixon trad is a little more delicate on the bottom notes than some, and gives a nice solid tone with just a whisper of breath. That shouldn’t be a problem with good breath control. But if you find there’s a really big difference in breath between the low D and E and the other notes just above (F#, G, etc.), then maybe you’re blowing those other notes too hard. Back off them a little, and try for a more even pressure across the entire first octave. You don’t have to blast a Dixon trad to sound good. 
When I first started whistling, I played all my notes way too loud. It was nice when I finally learned to “breathe into the whistle” in the lower octave–and the sound was better too.
Others, like your average monkey, would have probably learned this much sooner than I did.
I’ve been ruined by blowing into my bagpipe chanter I suppose- will try backing off on the whistle and see what it does. BTW- was wondering why the high D
(second octave) is fingered, at least according to the book I used, as all fingers on but L1- but if you overblow the low D, it sounds exactly the same to me as all finers on but L1- so why the different fingering??
If I get this right, when lifting L1, you’ll get a d’ with very little additional effortlessly, while with L1 on, you’ll have to blow a little harder (cleanly overblowing it, that is). I find myself using both fingerings, and I couldn’t say I have a single preference, and I haven’t encountered tuning issues (yet).
But I’m only a beginner… (and as a saxophonist, I know exactly what you’re talking about in terms of “ruining” one’s air control - the bigger horns need a whole lot of pressure, while the whistle needs delicacy).
M.
yeah, the trad can be delicate on the bottom notes as mtguru stated. going back and forth with my feadog pro can be fun in that regard.
as an aside, i picked up my mom’s chanter a few days ago and almost burst my eyeballs out my head trying to play the thing. 