I have a character who wants to describe how good his hearing is. I'm wondering if there are ways of measuring this (the way you can say you have 20/15 vision). He is a very scientific and analytical character, so I'm looking for something very clinical and technical that he can use to explain just how good his hearing is. It's okay if it's not colloquial or layman, in fact it's better if not. Any help would be much appreciated, thank you!