Great question, I think there are many aspects to a centered sound or a great, resonant sound.
If I recall correctly, I believe Greg describes in one of the videos that resonance is the optimum balance of Air and Shape / optimum efficiency–it’s when things feel and sound the best. Since it’s the optimum efficiency, it’s when playing is the easiest. I like this concept–that the most efficient is the best sounding; I believe that makes logical sense.
I don’t know about you, but I don’t get that sound everyday…I have good days, bad days and ok days…
Lately, it has occurred to me that I’ve stopped aiming for resonance–having the best sound / feeling, optimum efficiency…I’ve been more “results oriented” lately. Things have been going relatively good, so I kind of have been getting away with that… But, at the end of the day, we’re playing a musical instrument–that’s what it’s all about (music), not high notes, etc.