The audio may be inaudible but the "raster pattern" - the 15,600-cycles-per-second sweep signal...[rant alert]
I hear it all the time!
It is the same *issue I have with the "High Quality" sound of digital recording. The relatively slow sampling rate of first generation CD's at 40,000 (+-) that has to measure frequency, volume, wave shape etc... at that speed, it just disregards or has 100% error at frequencies over 16500. Shure it's missing the snap-crackle-pop and hiss of a standard cassette and/or vinil record player, but the musical sounds in those frequencies are just not there. A piano sounds like it is inside carboard box when it is digitally recorded. Cymbals sound like trash can lids (OK I'm exagerating)... you get the picture. People are now "trained" by not listening
to these "ambient sounds" so now they just don't listen
for them.
A prime example that almost everyone I know will tell me they can hear (sorry Dr.Bill): as you walk from a hallway into a room, or as you walk from a small room into an open space... even with no sound, you can sense the size of the room by the sounds you are or are not hearing... (do so with your eyes closed)!
Just another reason to enjoy live music... Now, If I could only get them to turn it down... grumble, mumble, fumble...[end rant]
