How to deal with my fear of large audiences?
If you haven't tried one of the beta blockers prescribed for performance anxiety/stage fright, they're worth looking into.  

For me, using propranolol before presentations has been much more helpful than I ever expected, and has even had carry over effects. (Basically I suck at talking to most people most of the time, but now I suck less!) Just having the experience of speaking without the physical effects of anxiety turned out to be powerful. Something about breaking the feedback loop, I guess -  

The fact that you mention your voice shaking, especially, makes me think beta blockers might help you.