I took a few lessons from Cat about two years before he passed away. He had me do the long tones in a harmon mute soft, like a whisper. He insisted on doing it on a harmon mute as soft as possible and would stop me if I got too loud at anytime. I eventually worked my way up to 20 minutes but I usually do 15. I don't have endurance problems and my chops are not mangled. I can finish a hard gig with my full range which is usually a consistent Bb above high 'c' guarenteed. Cat was big on practicing and warming up extremely soft and in the staff.