I had a masterclass in london with Andrew Ball in Nov 04, although I can't say I know anything of Nelita True to compare. He was very insightful and intelligent, and I found myself responding very positively to all of his comments. He understands music at a very deep level and is very astute. He talked a lot of orchestral colours and tone, and voices, and independence of voice. He's great for interpretation, lots of ideas and not unwilling to have a polite debate. I have heard, although- that he leaves technique aside somewhat. It is for this reason that I have chosen another teacher- I am desperately in need of better technique- so for the moment anyway, I have to focus on that. But if you were happy with your technique, then I have no problems recommending Andrew Ball as an outstanding teacher...