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No mention of how bad this must be for dogs and other animals that can hear better than humans.
I always wondered the same about ultrasonic parking/proximity sensors on cars.
Totally speculative territory, but I’ve had headaches when going to a shopping center since I was a kid. It’s infallible, one to two hours and my head is exploding. I’ve always attributed it to the noise, crowds and sensory overload but it never happens elsewhere. Could it be?
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I'm 30 with mild tinnitus and listen to music too loud but I can still hear CRT whine too, go figure.
Wait, people regularly just don’t hear it?
Of course, these days people also regularly don't hear it since CRTs are nearly all gone.
If this is the case, it would sound like there is no need to encode any information on the signal, just it's presence is enough to test the wiring is intact. I'm assuming this is so that if the PA is required for, say, an emergency broadcast, it is fit for purpose.
The presence of a <20Khz signal would imply that it was found that in whatever installation was being used that the bandwidth of the amplifiers or some other filter was attenuating the test tone too much to be received properly, so this bodge was put in place.
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even a headphone plugged in wrong is a good enough sensor to start. when it gets bad you start looking at designing your own ribbon elements and considering active pickups. when it gets worse you may find yourself deeply concerned about ADC and clock skew.
It doesn't matter what your microphone can do, because your sound card does the filtering and digitization.
see the mics that harmonica players lust after. "You traded the Cadillac for a microphone? ... I can see that."
I believe many sound chips still have ways around any pee-processing they may apply, might check the folks using them for low rate oscilloscope inputs
> Use it to deliver ads somehow Please don't write such things on the internet
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Wait, people regularly just don’t hear it?
You'll usually stop hearing the CRT whine in your 20s, 30s if you're lucky. It's at nearly 16KHz and the highest frequency you can hear always drops as you age. Of course, these days people also regularly don't hear it since CRTs are nearly all gone.
I live in Japan, Tokyo, and sometimes I come across these annoying/distracting high-pitched noises even in residential areas. They are a nuisance for bypassers too, if you've got ears young enough. But the residential areas don't have any problem with loitering youngsters, so I keep wondering if the noise is targeted against pests or wild animals. This article made me think if I should seriously start measuring the v…
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Can't speak for Tokyo, but there are streets in my American suburban neighborhood I avoid because of (presumably) animal-deterrent noises. I'm also 40, and surprisingly can still hear them - and an audiologist had my ears tested last month, and said my hearing is excellent for my age. Which is a bummer when I have to cycle around several blocks to avoid hearing the squeaks that are physically painful to my ears.
> squeaks that are physically painful Those may be covered under loud noise regulations, if the official measuring machinery has the cutoff frequency set high enough (no reason why not).