FM Radio transmitters broadcast a continuous 19 KHz pilot tone to indicate that it's a stereo broadcast. If it's present, then there's also a 38 KHz AM modulated carrier, which has the stereo information.
The main FM modulation is (Left + Right) audio channels - the baseband. The 38 KHz subcarrier is (Left - Right). Notice that the stereo information is likely to be higher noise, being AM and without a lot of power. So on weak FM broadcast signals, you're often better off setting your tuner to mono.
Some cruddy FM tuners don't properly filter out the 19Khz pilot tone, resulting in ear-ringing in the listener.
The unfiltered pilot tone was a problem when recording FM radio onto tape, beating against the bias tone and confusing Dolby NR into thinking there was constant sound.
High-end cassette decks had an "MPX Filter" which was a sharp 19kHz filter before the recording system.
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.
Going into Sears used to drive me nuts. My parents finally accepted that I was actually hearing something that they couldn’t, but it took a while.
I don’t know if it was the loss prevention system that was doing it, or what. All I could do was localize it down to being anywhere remotely close to the entrances. And the closer you got, the louder it got.
These days, my tinnitus is constantly ringing at about that same frequency. So, I would probably never be able to hear it again.
I had something similar, when i was young and walking the dog in the evening, i could here a high pitch tone if they had the tv on when i walked by houses.
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?
I've encountered this a few times in Tokyo myself; from memory at the very least outside of a mall in Shinjuku and outside of a building a block or two away from the Shibuya Scramble crossing. My traveling companion never noticed them until I pointed the sound out, so for those who find themselves in Japan pay attention if you notice a pressure in your ears and a high-frequency sound that seems to get more/less intense as you walk. If you follow the sound to its source you'll probably find that it seems to be coming from a metal trapezoidal horn, usually mounted from ceilings in places outside buildings from standard electrical junction box with exposed conduit. The sound itself is a constant, high frequency (18-20khz?) ring, and can get pretty intense as you approach the device.
I believe they're anti-loitering devices targeted at young people, who can hear a higher range of frequencies than older people. I've encountered them all over the US (if you're in the Bay, there's one mounted outside the Twin Peaks Tavern in Castro), though usually they pulse rather than emit a constant buzz. They're sporadic but common in Tokyo for sure, I encountered at least a dozen in the combined week or so I spent in various regions there. It was always creepy to me whenever I'd discover one, the sound was slightly nauseating if I ever got too close and left a strong negative impression, as though they were some sort of threat.
If anyone knows more specifics about these things btw, happy to have details. I spent a period of time trying to find the exact device but never could find any pictures of them, and unfortunately neglected to when I was actually in Japan.
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.
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).
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.
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.
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.
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 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.
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.
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.
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.
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.
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
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.
LED bulbs must drive them crazy. Many emit ultrasounds that I can hear when I'm next to such bulbs, like that of a vibrating capacitor (low quality AC filtering, low quality capacitor, or both).
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?
> .. 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..
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.
What does the author use to measure sound and create those graphs? I'm interested in automatically monitoring an annoying noise that's coming from a neighbour.
As others in the comments have already mentioned, Studio Six makes very nice Audio Tools (at least on iOS/Mac, not sure if they are also on Android). Their SMAART module is the cheapest way to get access to SMAART tools - which can be a thing in and of themselves. I use them to asses what's going on with live sound I occasionally mix. What's really nice is they calibrate fairly accurately to Apple hardware out of the box. More than accurate enough for my purposes.
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.
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
When I used to work with PA systems we had this really cool old-school looking impedance meter. We used to check the continuity of the PA like you do with a resistance meter in an electrical circuit.
I dont know much about analog audio but if I am remembering correctly, the device could inject a 1Khz tone that was only heard on speakers with impedance problems.
I'd like a way to use an array of mics and do some sort of visualization and video overlay to try to see and locate the sources of these kinds of high pitch sounds.
[+] [-] CliffStoll|1 year ago|reply
The main FM modulation is (Left + Right) audio channels - the baseband. The 38 KHz subcarrier is (Left - Right). Notice that the stereo information is likely to be higher noise, being AM and without a lot of power. So on weak FM broadcast signals, you're often better off setting your tuner to mono.
Some cruddy FM tuners don't properly filter out the 19Khz pilot tone, resulting in ear-ringing in the listener.
[+] [-] LeoPanthera|1 year ago|reply
High-end cassette decks had an "MPX Filter" which was a sharp 19kHz filter before the recording system.
[+] [-] skmurphy|1 year ago|reply
[+] [-] bradknowles|1 year ago|reply
I don’t know if it was the loss prevention system that was doing it, or what. All I could do was localize it down to being anywhere remotely close to the entrances. And the closer you got, the louder it got.
These days, my tinnitus is constantly ringing at about that same frequency. So, I would probably never be able to hear it again.
[+] [-] mateus1|1 year ago|reply
[+] [-] raverbashing|1 year ago|reply
But yes the old CRT whine I could definitely hear
[+] [-] GrumpyNl|1 year ago|reply
[+] [-] GolDDranks|1 year ago|reply
[+] [-] malwrar|1 year ago|reply
I believe they're anti-loitering devices targeted at young people, who can hear a higher range of frequencies than older people. I've encountered them all over the US (if you're in the Bay, there's one mounted outside the Twin Peaks Tavern in Castro), though usually they pulse rather than emit a constant buzz. They're sporadic but common in Tokyo for sure, I encountered at least a dozen in the combined week or so I spent in various regions there. It was always creepy to me whenever I'd discover one, the sound was slightly nauseating if I ever got too close and left a strong negative impression, as though they were some sort of threat.
If anyone knows more specifics about these things btw, happy to have details. I spent a period of time trying to find the exact device but never could find any pictures of them, and unfortunately neglected to when I was actually in Japan.
[+] [-] h2odragon|1 year ago|reply
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...
[+] [-] modeless|1 year ago|reply
[+] [-] londons_explore|1 year ago|reply
[+] [-] unknown|1 year ago|reply
[deleted]
[+] [-] pants2|1 year ago|reply
[+] [-] mholt|1 year ago|reply
[+] [-] louthy|1 year ago|reply
[+] [-] tlb|1 year ago|reply
[+] [-] kurthr|1 year ago|reply
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.
[+] [-] doughecka|1 year ago|reply
[+] [-] spondylosaurus|1 year ago|reply
[+] [-] liminalsunset|1 year ago|reply
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.
[+] [-] leviathant|1 year ago|reply
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.
[+] [-] matteason|1 year ago|reply
[0] https://old.reddit.com/r/TaylorSwift/comments/17iv3r2/for_pe...
[+] [-] ryandrake|1 year ago|reply
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.
[+] [-] KennyBlanken|1 year ago|reply
[+] [-] lgats|1 year ago|reply
[+] [-] fullspectrumdev|1 year ago|reply
They were quite expensive and I know of a few people who got annoyed and specifically vandalised them due to the annoying sound.
[+] [-] i80and|1 year ago|reply
[+] [-] michaelcampbell|1 year ago|reply
[+] [-] s1mon|1 year ago|reply
[+] [-] amelius|1 year ago|reply
[+] [-] _Microft|1 year ago|reply
[+] [-] drtgh|1 year ago|reply
[+] [-] yard2010|1 year ago|reply
Please don't write such things on the internet
[+] [-] ale42|1 year ago|reply
[+] [-] MichaelMug|1 year ago|reply
[+] [-] ricardobeat|1 year ago|reply
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?
[+] [-] LorenPechtel|1 year ago|reply
[+] [-] e40|1 year ago|reply
[+] [-] Ylpertnodi|1 year ago|reply
[+] [-] jszymborski|1 year ago|reply
[+] [-] transpute|1 year ago|reply
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.
[+] [-] fredthedeadhead|1 year ago|reply
[+] [-] EricE|1 year ago|reply
[+] [-] cesaref|1 year ago|reply
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.
[+] [-] mannyv|1 year ago|reply
[+] [-] instagib|1 year ago|reply
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...
[+] [-] lomase|1 year ago|reply
I dont know much about analog audio but if I am remembering correctly, the device could inject a 1Khz tone that was only heard on speakers with impedance problems.
https://toa.co.id/product/zm-104a-impedance-meter
[+] [-] _spduchamp|1 year ago|reply
[+] [-] Waterluvian|1 year ago|reply