[HN Gopher] Ultrasonic investigations in shopping centres
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Ultrasonic investigations in shopping centres
Author : GolDDranks
Score : 187 points
Date : 2024-06-09 14:35 UTC (8 hours ago)
(HTM) web link (www.windytan.com)
(TXT) w3m dump (www.windytan.com)
| GolDDranks wrote:
| 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 volumes and
| frequencies objectively. What kind of equipment would you need to
| get some data to get started with?
| h2odragon wrote:
| > 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...
| datameta wrote:
| And you might accidentally get into field recording and
| manipulating sound with a portable modular synth... Oops
| immibis wrote:
| Normal computer recording only goes up to 48kHz (24kHz
| Nyquist rate, with analog filters lower than that to prevent
| aliasing) but high-quality equipment might support 96kHz or
| even 192kHz.
| h2odragon wrote:
| 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.
| immibis wrote:
| It doesn't matter what your microphone can do, because
| your sound card does the filtering and digitization.
| h2odragon wrote:
| it might; depending on your goals: microphones color the
| sound and their limits can be as valuable as their
| capabilities, in the right context.
|
| 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
| dylan604 wrote:
| > but then you'll be constantly tempted by better...
|
| this is a likely outcome for any new hobby
| GolDDranks wrote:
| 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
| smartphone apps are capable of consuming the mic input
| unfiltered? (Never tried recording APIs for that purpose)
| lanthade wrote:
| Studio Six Digital makes the very useful app AudioTools.
| They test all iOS devices to create generic profiles for
| the built in mics. They've found them to be very consistent
| which is kind of remarkable for a consumer cell phone
| device.
|
| More info here: https://studiosixdigital.com/audio-
| hardware/generic-audio-ha...
| modeless wrote:
| 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.
| pavel_lishin wrote:
| 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.
| B1FF_PSUVM wrote:
| > 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).
| pavel_lishin wrote:
| Yeah, maybe. But the hassle of trying to convince the
| town this house is in - which isn't my town - to do
| something about it is significantly more difficult than
| just riding my bike around the place.
| nicolas_t wrote:
| I've always wondered about that. I'm also bothered when
| walking around Tokyo (it's very prevalent in Ginza for some
| reason). I've also seen it in other cities in Japan but I've
| never had that issue in other cities in Asia (Hong Kong,
| Shanghai, Bangkok, etc..)
|
| 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.
| mholt wrote:
| Those are probably vole deterrents.
| louthy wrote:
| Omnidirectional reference microphone would do the job.
| londons_explore wrote:
| There are lots of "rat deterrant" devices which emit varying
| tones 15-20 kHz. they often emit chirps or frequency sweeps.
| Sometimes always-on, sometimes with an IR sensor (in battery
| powered versions).
| spondylosaurus wrote:
| 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.
| liminalsunset wrote:
| 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 realized
| that all of the versions have this.
|
| The reason for this is because at concerts, you can buy a piece
| of merch called a lightstick. Essentially, it is a STM32 and a
| mems microphone that is demodulating the carrier signal, so it
| can flash in time with the music. The tone has to be
| <ultrasonic because it has to work with consumer speakers and
| the mic in the device.
|
| I assume the theory goes that anyone who has been to enough
| concerts to have a lightstick is no longer capable of hearing
| the noise.
| kmeisthax wrote:
| Alternatively the sound is in there deliberately so that if
| you have a lightstick it'll start playing in time with the
| music.
| matteason wrote:
| This happened recently on Taylor Swift's rerecording of 1989 -
| a persistent tone at 15KHz on multiple tracks [0]. The Taylor's
| Version records have to be some of the most carefully-produced
| albums around, given that the goal is to accurately reproduce
| existing recordings, so it's amazing that it made the final
| release.
|
| [0]
| https://old.reddit.com/r/TaylorSwift/comments/17iv3r2/for_pe...
| mrob wrote:
| It's surprisingly common in older music. I assume it's
| because recording studios used to run SD CRTs and everybody
| working there had already lost their high-frequency hearing.
| A 15.68kHz (mid way between PAL and NTSC horizontal refresh
| frequencies to remove both of them) notch filter fixes the
| problem in most cases.
| lgats wrote:
| https://www.youtube.com/watch?v=QtbxWas-3oM
| leviathant wrote:
| Sometimes it's old ears, sometimes it's the people in the room
| being oblivious to it from hearing it too much. I tell the
| story a lot about kind of the inverse of this - I was mixing my
| band's (terrible) recording, and during a weekend of mixing, I
| heard the squeak from my cheap kick pedal, like an icepick to
| the brain, piercing through the mix. I did my darnedest to EQ
| it out, and felt pretty good about it in the end.
|
| On my Monday morning drive to work, I put on a CD by the band
| Cake, an album I'd listened to dozens, if not hundreds of times
| at this point, and would you believe that now, piercing through
| the mix, I heard the squeak of the drummer's kick pedal. Never
| noticed it before, but because I was so focused on those
| frequencies for two days straight, now it was all I could hear.
|
| I switched to listening to purely electronic music that month,
| and I never noticed squeaky kick drums in studio recordings
| again.
| alamortsubite wrote:
| Thanks for not telling us the track! I probably love that
| song, whichever it is, and wish to remain ignorant.
| KennyBlanken wrote:
| I've noticed some FM stations have an odd metallic ringing
| noise in the background - especially country for some reason.
| I'm fairly certain it isn't intentional.
| ryandrake wrote:
| 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 single frequency buzz or carrier wave. It
| changes along with the pitch of the lyrics and clearly some
| kind of filtering they're doing to the voices. Either that or
| I'm paranoid and hearing things.
| abdulhaq wrote:
| it's autotune
| ornornor wrote:
| What a plague this thing is :(
| Nition wrote:
| The other comment is right that autotune is almost always
| present in recent pop vocals - even when the singer is
| excellent, a little bit is now commonly added to give it that
| certain sound.
|
| Having said that, I think what you might be hearing is
| actually another modern trend - which is just boosting the
| high frequencies in the vocal a lot. Pop vocals right now are
| mixed very 'bright', sometimes almost painfully so.
|
| Also common to actually have multiple vocal tracks. Sometimes
| just a double singing the same thing, but sometimes it can be
| pitched up or down an octave, and I've also seen "whisper"
| tracks where a whispered vocal is layered with the main one
| to give it even more of that bright breathy sound.
| amelius wrote:
| No mention of how bad this must be for dogs and other animals
| that can hear better than humans.
| _Microft wrote:
| I always wondered the same about ultrasonic parking/proximity
| sensors on cars.
| HeatrayEnjoyer wrote:
| What cars produce ultrasound? I thought radar is used.
| matteason wrote:
| Wikipedia says both ultrasonic and electromagnetic are
| used: https://en.wikipedia.org/wiki/Parking_sensor
|
| One of the references is for a Mercedes system that uses
| ultrasound
| buildsjets wrote:
| Every single car from every manufacturer that has PDC
| sensors in the bumper, which are typically visible as 4
| circular sensors on the surface of the bumper.
| ptero wrote:
| Most cars have ultrasonic sensors for parking and radar for
| longer range detection, such as cruise control.
| ornornor wrote:
| I hear some car alarm sensors when passing by, the ones
| that will trigger when someone is about to park too close
| and hit the armed car.
| houseplant wrote:
| induction stovetops create extremely loud high pitched
| noises, some get up to 100+ decibels. You can't "hear" it but
| at higher heat levels you can definitely "feel" it in your
| ears.
| hehdhdjehehegwv wrote:
| It's been used for ads for years.
| pavel_lishin wrote:
| How so?
| paulmd wrote:
| https://en.wikipedia.org/wiki/Cross-
| device_tracking#Ultrason...
| xphilter wrote:
| I brought some class actions years ago alleging the unlawful
| use of this tech for essentially ads purposes:
| https://topclassactions.com/lawsuit-settlements/lawsuit-
| news...
|
| and https://www.freeadvice.com/legal/lisnr-responds-to-
| lawsuit-t...
| jszymborski wrote:
| Oona's blog posts are consistently bangers; always a treat when
| she posts a new one.
| tlb wrote:
| 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.
| kurthr wrote:
| I'd also be suspicious of this. You can also get a lot of
| beating artifacts from having many amplifiers in close
| proximity. If the speakers were still larger "mid-range" horns
| as were seen in decades past, this also might be less of an
| issue (low efficiency above 10kHz), but for cost/aesthetic
| reasons the speakers have shrunk quite a bit so they no longer
| mechanically filter much.
|
| 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.
| instagib wrote:
| Bistatic 0. one transmitter + two receivers. Very fun topic as I
| worked on a few and sync them up as the transmitter radar needs
| to connect to the second receiver radar (usually a full radar for
| redundancy). Multistatic is fun also as they employ many covert
| receivers. Had many war game scenario conversations about the
| setups.
|
| 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...
| fullspectrumdev wrote:
| I had almost forgotten about the "Mosquito" devices for deterring
| youths that became ubiquitous in some areas during the late
| 2000's and early 2010's.
|
| They were quite expensive and I know of a few people who got
| annoyed and specifically vandalised them due to the annoying
| sound.
| i80and wrote:
| I'm glad those seem to have mostly faded away? The installation
| of them especially in spaces open to the general public has
| always struck me as deeply sick and antisocial
| fullspectrumdev wrote:
| There's still a few around where I live, way less than before
| though and I think it's old installations that somehow still
| function instead of "net new".
|
| What's awfully irritating is that I can still hear them. I'm
| in my 30's with pretty gnarly hearing damage, and can _still_
| hear that frequency range.
| houseplant wrote:
| I believe they were harming birds and insects, but I don't
| think someone using a mosquito tone to deter human beings
| cares much for wildlife health
| mannyv wrote:
| Cruise ships do this. It drove my kids crazy.
| doughecka wrote:
| I work for a manufacturer of PA systems, our amplifiers only do a
| periodic test every few minutes, one channel at a time. We
| measure the current the speaker circuit draws, and if that
| changes drastically we know something is wrong.
| transpute wrote:
| _> .. 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 degC 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._
| skmurphy wrote:
| 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.
| raverbashing wrote:
| 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
| skmurphy wrote:
| 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.
| metabagel wrote:
| One thing that can help is pressing the turn signal lever
| with less force than is needed to latch it. This should
| cause the indicator to flash three times and then stop.
| It's an operating mode I wasn't aware of for decades.
| jimmaswell wrote:
| I'm 30 with mild tinnitus and listen to music too loud but I
| can still hear CRT whine too, go figure.
| gocartStatue wrote:
| Wait, people regularly just don't hear it?
| Nition wrote:
| 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.
| ikari_pl wrote:
| 37 here. Definitely still hear if the CRT is on. I have a
| few 8bits.
| Nition wrote:
| Yeah, that one's a bit lower. 15.625kHz or 15.75kHz depending
| on your region.
| imabotbeep2937 wrote:
| I've been tested to 22+kHz, autistic, and older. It was the
| worst era.
|
| Some of the awful roars of noise I've heard while older
| people called me a weirdo. CRTs, early checkout scanners,
| some audio systems.
|
| And back when "as seen on TV" electronic dog whistle trainers
| were all the rage? Torture.
| yard2010 wrote:
| > Use it to deliver ads somehow
|
| Please don't write such things on the internet
| MichaelMug wrote:
| It's clearly written it's an idea. I don't know what you're
| implying here.
| jfengel wrote:
| He's saying not to give them any ideas.
| ale42 wrote:
| Having read this blog in the past, I imagine the author was
| sarcastic on this one.
| ricardobeat wrote:
| 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?
| e40 wrote:
| Smell, too. Clothes stores always smelled horrible to me and
| almost always gave me a headache.
| cesaref wrote:
| From the description of the product, I think the intention is
| that the tone is received electrically at the end of a cable run,
| so receipt of the tone indicates continuity of the speaker
| cabling. This high frequency has been chosen to ensure that it is
| low enough to be amplified and transmitted along with the audio
| content, and is high enough to be attenuated by the tweeters (so
| little energy is transmitted), and high enough in frequency so
| that whatever is emitted by the tweeters will be inaudible.
|
| 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.
| s1mon wrote:
| I searched the article for "occupancy" and nothing. These
| ultrasonic tones are most likely ultrasonic occupancy sensors
| used for lighting and/or security. Typically they're 25kHz or 40
| kHz (i.e. out of normal human hearing range), but it's possible
| that they are measuring some subharmonics of the sensors. I've
| certainly encountered ones that have mechanical issues and will
| spit out frequencies that I can hear too well.
| Waterluvian wrote:
| I wonder how much spectrum screaming we're doing from the
| perspective of other species' sight and sound.
| Havoc wrote:
| > I might have been scrolling through the audio spectrum while
| waiting for the underground train;
|
| What gadget is this person using for this? And audio-y flipper
| one of sorts?
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