I accomplished a major hurdle of mine and finally can produce a decent tone on my trumpet. My teacher was quite pleased. I have a problem though of the tone decaying really really quickly about 10-15 minutes. I can do warm-ups or go directly to music and get a good tone , so I know the problem isn't over warming-up. Is this a lip strength issue that has to be built up over time because my chops still feel fine no matter how long I play for(within reason). My teacher says it more of a mental problem then a physical problem. Other than that he said he never really encountered an issue like this. Any thoughts? I simply just think of a trumpet player and try to emulate their tone to the best of my ability.