Great to hear from another terp, Miabeth! You're absolutely right that there is nowhere near enough training for voicing in most ITP's. Like all skills related to interpreting, it is best learned by doing, but if one doesn't get enough practice before being thrown into the "real world" it can be very difficult gaining the necessary confidence.
In fact, I think that's a lot of what's involved with voicing - self-confidence. We must sound comfortable when voicing, and even if we're understanding perfectly, if we're not sure of our skills it will be very difficult to put it out there with the appropriate register.
