I have been playing Euphonium for a few years and I am wondering, I can with some difficulty consistently play up to concert high Bb and C. My question is how can I make these upper notes more Comfortable to play and get a more full sound on them? I try and hold long tones on them for a few weeks but haven't felt or heard much improvement. Does anyone have any suggestions for making high range more comfortable as oppose to trying to expand my range?