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I always wondered the same about ultrasonic parking/proximity sensors on cars.
What cars produce ultrasound? I thought radar is used.
It’s been used for ads for years.
How so?
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> what kind of equipment Any microphone hooked up to a laptop with a microphone input. Or a phone running some audio spectrogram app. Getting started is very easy, but then you'll be constantly tempted by better sensors, more sensors, more channels, more analysis...
I assumed that most of the normal consumer-level stuff is (perhaps very deliberately) insensitive to sounds that human ears are insensitive to? The common codecs, for sure, tend to have rather harsh cutoffs around 20kHz (the common sampling rates being 44 or 48kHz, and the Nyquist frequency half of that, 22-24kHz, so you have to start filtering well before?) Plus, I'd rather not walk around with a laptop. But perhaps…
More info here: https://studiosixdigital.com/audio-hardware/generic-audio-ha...
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…
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…
I came across some of these in Tokyo recently as well. Super annoying, and I'm 40. I thought I'd be immune by now. I assumed they were intended to drive away cats or rats or mosquitos.
I'm 40 too but as a kid, I was very bothered by the high pitch wine of the tv turning on, so I'm guessing I've always been rather sensitive.
Have you ever listened to a badly mixed song with a persistent high-pitched whine undercutting part (or all) of it? Certainly that's not on purpose either, but I doubt anystudio equipment is giving off an intentional "test" whine either, so I've always wondered how that ends up happening.
I've got an example of this: Some Blackpink songs (cannot remember which ones, possibly Playing With Fire or DDU-DDU-DDU) were mastered and released on Spotify/iTunes [unsure if has been removed now] with a 18-19kHz carrier tone (iirc it was actually a number of tones) modulated. The signal was very loud. I first noticed this in a friend's car and assumed it was because the song was ripped from YouTube, but later rea…
Maybe they’re getting a bistatic return with multiple microphones separated in distance enough to be significant.
Ultrasonic frequencies generally start at around 20,000 Hz (20 kHz) and can extend up to several gigahertz (GHz). 1
0. https://en.m.wikipedia.org/wiki/Bistatic_radar
1. https://www.rfcafe.com/references/general/ultrasonic-spectru...
Has the hypothesis that this is noise from a class-D amplifier (which I assume most commercial speakers use) been eliminated? Those generally switch at MHz frequencies, but have subharmonics all over the place except the ones that have been carefully eliminated by filtering. I wouldn't be too surprised if there was a cheap brand of class-D amplifier that had a 20 kHz tone.
If the problem was something everyone could hear it would likely be fixed, but since it's a minority, it's likely to persist.
One other possibility for active US is crowd tracking. I've seen solutions that monitor # people and walking speed at doorways using ultrasonics. A lot of "one way" doors also use simple US detectors.