One of the problems with hearing loss is that it's difficult to determine where you're trying to get to. They can give you read-outs at the hearing-aid place, but if they adjusted the aids to that, it would be too painful to listen to. (I.e., it takes time for your brain to adjust). I don't put in my hearing aids at a concert (some people do); so how would I determine the precise sound I'm looking for at home? (For some things, you can ask a simple question: do I understand what people are saying? like, those kids in the back of the classroom. And you can adjust your hearing aids such that you suddenly CAN understand them. Trying to hear music, however--that's a completely different animal.)
