Thirty-some years ago I used to have east access to a "test" of my HF
hearing! I worked for Rogers Toronto as a "cable guy"...and we were just
introducing "cordless" TV convertors. The first generation of those used
HF sound 915 KHz plus) which was supposedly beyond Human hearing;
however, I could hear most of the tones!

I did have one unusual servicwe complaint, though; a lady told ne that
every time she changed channels with her new converterm her
cat bit her.!

Steven C. Barr