In terms of sound one could point toward a whistle for understanding the meaning of this word.
Aboard large ships of times past these things were supposed to be loud enough to keep everyone abreast of critically important information.
Police forces everywhere use them.
The military use them. Athletic Coaches and Referees use them.
The ultimate shrill must be the dog whistle, which we are not supposed to be able to hear.
The high pitch implication for this word gives us a good place to start talking about when Shrill is not a bad thing.
More on that later.