Hi, I've been playing the trumpet for about twelve years and my problem si fast single tonguing. I asked my teacher and he said it's because I don't touch by tip of tongue behind the front teeth but between them and slightly touching a tip of my upper lip. It breaks my the tone and I can't tongue fast. I've tried, as my teacher told me, buzzing on my lips without the trumpet and I can articulate 'Tu' with my tounge behind the teeth but once I put the mouthpiece on my lips I can't get the tongue there, only between my teeth. I don't know what to do to get rid of this habit.