"I used to be able to tell whether a CRT monitor or TV was on or off being in a different room. I guess I could hear the 50Hz?"
I am able to do this as well and usually attribute that to the fact that I grew up in a household without a TV. I could enter a house and immediately tell whether someone watched TV in the basement. Now, the question I have that I never got around asking:
Is this due to most people just not being able to hear those frequencies or just the fact that this sound is so common that most people just don't notice it anymore?
I could too but dont think I can anymore as have got older, though hard to find a crt to check. Suspect a lot of people just could never hear that high.
I grew up with TVs and still can hear most of the CRT sets. It's because, IIRC, the horizontal sync frequency is around 15KHz which is higher than what most people hear. The sound gets significantly louder when the TV loses signal. The same happens with NTSC/PAL frequency computer monitors (I restore and collect vintage computers, so I have a healthy collection of those).
Oddly, some higher resolution screens (XGA and above) also emit a high pitch noise. Unless there is some frequency multiplication going on, they shouldn't.
"I used to be able to tell whether a CRT monitor or TV was on or off being in a different room. I guess I could hear the 50Hz?"
I am able to do this as well and usually attribute that to the fact that I grew up in a household without a TV. I could enter a house and immediately tell whether someone watched TV in the basement. Now, the question I have that I never got around asking:
Is this due to most people just not being able to hear those frequencies or just the fact that this sound is so common that most people just don't notice it anymore?