Speaking of what you can hear and what you can't,
I'm very good at the low end but, for years I've known my high frequency hearing is shot.
I'm told that's pretty normal as you age however if you've ever had a hearing test, It's disheartening to see the results.
For somebody trying to be a musician and mixer It's a bit scary for me to realize how much I'm missing.
There are a few hearing tests out there, this one is just a continuous sweep low - high:
Probably a dozen years ago, while my youngest was still living at home, he and a buddy were going through some kind of online hearing test, mapping individual hearing up to 20khz. I walked into his room and mentioned about how my hearing was shot from my misspent youth of standing in front of very large amplifiers. They had me clamp on the headphones (Koss Pro-4AA), which should be reasonably flat to about 16khz. The test started at 20Khz and each tone stepped down. I was supposed to let them know when I finally heard a tone. I had my back turned to them, so I couldn't see what they were doing. After almost a minute I could hear them laughing, so I pulled off the phones to ask what was so funny.
They said they were down to 14Khz and it was so loud they could hear it outside my headphones (which are closed back and very well isolated), while I heard nothing.
I've since checked it several times and it's down to nearly 10Khz top end. The funny thing is, while I can't hear higher test tones, I can certainly hear the difference in coloration change when low-pass filters are applied to music recordings with healthy high-end overtones. Go figure!