Anyway...
I've recently come to the point where I can play the whole horn with a fair amount of ease. From pedal Bb to double-high Bb (and above and below) and it feels pretty effortless. And let me tell you, that's a wonderful feeling. Plus, I don't feel as much difference in effort between the low notes and the high notes anymore. High notes take much less effort. And I can do it with tone, and my facility is easier/better, too. In fact, the facility part is really fun.
So I asked myself, what changed? Why did I sort of suddenly get better at these things? And then I paid attention.
Best I can tell, I'm doing two things slightly differently than I was earlier, and I'm consciously doing one other thing slightly more than I used to. I emphasize slightly because these are all very small changes. I'm reminded of the movie "Contact," where Ellie's dad tells her, "Small moves, Ellie. Small moves." And that was the most important message of the movie.
The two things I'm doing slightly differently are:
1. I'm keeping my corners slightly tighter and pushing more toward the center. When I say corners I'm not talking about the very edge where the lips meet, but the "corners" that are the focus spots more toward the mouthpiece rim. And when I say pushing more toward the center, I say that to distinguish it from pursing the lips forward.
2. As I get higher I'm changing the angle of the horn slightly downward. This last was a suggestion from Dave and Doug, which I rejected at first because they had me going down and to the left and that wasn't working for me. But just downward a little bit as I ascend (and back, descending) feels pretty darn good. And it also helped with the next part.
I have to emphasize again that these are tiny, tiny changes. But they've made a noticeable impact.
And the thing I'm doing slightly more than I've been doing is to minimize the pressure I use. Doing that makes everything easier, top to bottom. Most of us, including me, have this intuitive thing that says to use more pressure going high, and if we try to do it without pressure we fail miserably, and see that as proof that using the pressure is helpful. But what I've found is that backing off as far as I could made me become much more efficient with my mechanics, with the result being that eventually my high notes actually became easier than ever, and without using pressure it wasn't as fatigueing.
Anyway, putting those three things together resulted in a kind of gestalt, where the amount of improvement was greater than the amount of change.
Does this make sense to anyone? I anticipate people telling me I'm doing it all wrong!
