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Ultrasonic investigations in shopping centres

windytan.com

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Re: Ultrasonic investigations in shopping centres

#41

Post by transpute »

> .. there's a clear Doppler shift in the reverb. The frequency shift goes from positive to negative at the same moment that the scooter passes us, seen as the wideband wheel noise changing color.. The speed of sound at 15 °C is 340 m/s. The maximum Doppler shift here seems to be 350 Hz. Plugging all these into the equation we get 11 km/h, which sounds like a realistic speed for a scooter.. Automated speed trap in the car park..

Doppler radar, https://en.wikipedia.org/wiki/Doppler_radar, also applies to WiFi reflections, which can be visualized, https://www.youtube.com/watch?v=g3LT_b6K0Mc.

Upcoming 2024 "AI" PCs, tablets and phones with NPUs and WiFi 7 can use machine learning and doppler reflections to infer human activity in 3-D space (proximity, movement, heart rate, gestures), via IEEE 802.11bf WiFi Sensing, https://www.technologyreview.com/2024/02/27/1088154/wifi-sen...

> Soon, thanks to better algorithms and more standardized chip designs, [WiFi] could be invisibly monitoring our day-to-day movements for all sorts of surprising—and sometimes alarming—purposes. Yes, it could track your breathing. It could monitor for falls. It may make buildings smarter, and increase energy efficiency by tracking where people are. The flip side of this, however, is that it could also be used for any number of more nefarious purposes. Someone outside your home could potentially tell when it’s vacant, or see what you are doing inside.

Re: Ultrasonic investigations in shopping centres

#42

Post by abdulhaq »

ryandrake wrote: post #40
spondylosaurus wrote: post #5

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.

Whenever my daughter puts on recent pop music, I can tell instantly. Every pop song singer seems to have their voices artificially boosted into one or two higher harmonics. It's hard to describe in words but instead of the singer singing a single note, it's as if she (and it's very evident with female singers) has some very, very high pitched harmony automatically added, which lasts the whole song. It's not like a si…

it's autotune

Re: Ultrasonic investigations in shopping centres

#43

Post by [deleted] »

GolDDranks wrote: post #2

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…

[deleted]

Re: Ultrasonic investigations in shopping centres

#44

Post by skmurphy »

Very interesting. I can remember being able to hear a high pitched tone when I was 4-6 shopping with my mother in department stores that seemed to get louder when we approached flush mounted speakers in the ceiling. This article measures the frequencies and explains it's a normally operating feature of the systems.

Re: Ultrasonic investigations in shopping centres

#45

Post by raverbashing »

skmurphy wrote: post #44

Very interesting. I can remember being able to hear a high pitched tone when I was 4-6 shopping with my mother in department stores that seemed to get louder when we approached flush mounted speakers in the ceiling. This article measures the frequencies and explains it's a normally operating feature of the systems.

I'm not sure I ever managed to hear a 19kHz tone, but I'd say it might have been possible (or the tone was a lower frequency one).

But yes the old CRT whine I could definitely hear

Re: Ultrasonic investigations in shopping centres

#46

Post by skmurphy »

raverbashing wrote: post #45
skmurphy wrote: post #44

Very interesting. I can remember being able to hear a high pitched tone when I was 4-6 shopping with my mother in department stores that seemed to get louder when we approached flush mounted speakers in the ceiling. This article measures the frequencies and explains it's a normally operating feature of the systems.

I'm not sure I ever managed to hear a 19kHz tone, but I'd say it might have been possible (or the tone was a lower frequency one). But yes the old CRT whine I could definitely hear

I was young. My mother could not hear it and thought I was just being annoying. This is several decades ago, now I can barely hear my turn signal blinker and am preparing to emulate my father's practice of driving a few miles with his blinker on after signalling a lane change.

Re: Ultrasonic investigations in shopping centres

#48

Post by jimmaswell »

raverbashing wrote: post #45
skmurphy wrote: post #44

Very interesting. I can remember being able to hear a high pitched tone when I was 4-6 shopping with my mother in department stores that seemed to get louder when we approached flush mounted speakers in the ceiling. This article measures the frequencies and explains it's a normally operating feature of the systems.

I'm not sure I ever managed to hear a 19kHz tone, but I'd say it might have been possible (or the tone was a lower frequency one). But yes the old CRT whine I could definitely hear

I'm 30 with mild tinnitus and listen to music too loud but I can still hear CRT whine too, go figure.

Re: Ultrasonic investigations in shopping centres

#49

Post by B1FF_PSUVM »

pavel_lishin wrote: post #18
modeless wrote: post #4

Earlier quoted context omitted.

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.

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).

Re: Ultrasonic investigations in shopping centres

#50

Post by Nition »

raverbashing wrote: post #45
skmurphy wrote: post #44

Very interesting. I can remember being able to hear a high pitched tone when I was 4-6 shopping with my mother in department stores that seemed to get louder when we approached flush mounted speakers in the ceiling. This article measures the frequencies and explains it's a normally operating feature of the systems.

I'm not sure I ever managed to hear a 19kHz tone, but I'd say it might have been possible (or the tone was a lower frequency one). But yes the old CRT whine I could definitely hear

Yeah, that one's a bit lower. 15.625kHz or 15.75kHz depending on your region.
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