from Hacker News

The Hummingbird Clock: date videos by background mains hum

by wodow on 10/9/22, 1:49 PM with 148 comments

• by unvs on 10/9/22, 4:04 PM

  There's an artist called Øystein Wyller Odden that works with mains hum. I find it pretty fascinating:

  Kraftbalanse is a musical translation of the hum from the mains; i. e. the frequency of the alternating current. The piece is based on the fact that this frequency is not stable, it fluctuates subtly around 50 Hz as a direct result of supply and demand in the power market.

  The composition consists of a self-resonating piano that is tuned to resonate on 50 hz and overtones of 50 hz (100 Hz, 150 Hz, 200 Hz etc.) The piano is fitted with vibration-elements – transducers – plugged directly into the electrical grid, causing the resonance and timbre of the piano to change with the fluctuations on the power market.

  The piano is accompanied by a string octet. The musicians are equipped with voltmeters that measure the frequency of the current in real time, as well as a score of instructions on how to respond to changes in this frequency.

  https://vimeo.com/370554138

• by helsinkiandrew on 10/9/22, 3:11 PM

  This 5 minute video from Tom Scott on YouTube is a good overview without that annoying hum:

  https://www.youtube.com/watch?v=e0elNU0iOMY

• by zxcvgm on 10/9/22, 2:27 PM

  Tom Scott did a video about this topic in 2021: https://www.youtube.com/watch?v=e0elNU0iOMY

• by tgsovlerkhgsel on 10/9/22, 3:15 PM

  I was excited to possibly see this provided as an open source tool or at least an automated service, but the site offers a form to request dating, which looks like a manual process. That's not really making it available to everyone.

• by Aachen on 10/9/22, 2:32 PM

  Warning: site autoplays a loud (presumably 50Hz) buzz...

• by quacksilver on 10/9/22, 6:12 PM

  This is widely known and allegedly used by law enforcement forensics etc.

  I have often thought about building a SaaS service that strips or adds the correct hum and harmonics to videos if you wanted to plant some false evidence or make a good deepfake. If it failed to make much cash I could put it on github for free.

  I have never quite found the time and openly doing that kind of thing is probably likely to attract undesirable attention.

• by anfractuosity on 10/9/22, 5:21 PM

  I'm surprised when it says "the exact same buzz can be heard at the exact same moment nationwide from Land's End to John o' Groats", I didn't realise it would be the same across the UK.

  I played a little with a transformer to take 230VAC -> 12VAC, and then using a potentiometer to feed the waveform into a soundcard. But I'm not sure the sample rate of the soundcard was high enough to accurately measure the times between 0 crossings.

  Photo of the very messy setup - https://www.anfractuosity.com/files/hum.jpg

• by jsjohnst on 10/9/22, 3:05 PM

  I don’t see how this can be used to “authenticate” a video. If I’m already editing the video anyway, could you filter the original hum out and replace it with the correct frequency for the time you wanted to fake? There’s got to be a margin of error anyway, so would seem very possible to fake unless I’m missing something.

• by pugworthy on 10/9/22, 5:44 PM

  That clock graph is fantastic.

  I haven't let it run long enough to see if the minute and hour hands do the same line, but if so what a great way to show minute, hour, and day (24 hour clock) trends.

• by evan_ on 10/9/22, 5:02 PM

  This would be good to use for syncing clips from multiple cameras in video editing packages

• by ok123456 on 10/9/22, 5:58 PM

  Filtering out 50Hz/60Hz noise as a band stop filter is a common audio post processing step, precisely because it's noise from the power system.

  I wouldn't be surprised if there were phones that automatically applied this filter.

• by paulkrush on 10/9/22, 3:04 PM

  How far do I or can I transmit into the grid? How far do load changes from my house transfer into the grid? Surely my neighbors could detect 1us spikes not big enough to pop mains at say 800hz?

• by GranPC on 10/9/22, 3:21 PM

  How does this auto-play sound without user interaction?

• by actionfromafar on 10/10/22, 11:00 AM

  I wonder how much of this historic data could be crowdsourced from recordings of radio shows, VHS taped newscasts etc.

  Audio dendrology, if you will.

• by remram on 10/9/22, 10:54 PM

  How difficult would it be to defeat that completely or fake a different date? If people can find subtle noise that fools computer vision algorithms, can something similar not be applied to this?

  A band-pass filter might be a little simplistic because it's never 100% attenuated and the harmonics persist, so given a long enough sample you would probably be able to correlate. But perhaps more advanced techniques exist, if you know exactly what the other party is looking for?

• by BuildTheRobots on 10/10/22, 11:27 AM

  Does anyone know what resolution of frequency data I'd need to be recording to be able to date a recording myself?

  After reading this, I remembered that I have an IoTaWatt throwing mains voltage and frequency into Influx every second or so, but I've got no idea if this would be high enough resolution to match against a recording (or even how one would go about doing it).

• by LinuxBender on 10/9/22, 6:32 PM

  Interesting. What effect if any will my home being entirely on off-grid inverter 100% of the time have on this? I use Solar/Commercial/Generator -> DC Power Supplies / Charge Controllers -> Inverter -> Non-Resistive loads. My inverters are entirely isolated from commercial power. Can someone perhaps tell the make/model of my inverter?

• by sandworm101 on 10/9/22, 2:29 PM

  How many videos, outside fixed webcams, come from devices plugged into the wall? I venture that 99.99% of videos where the timestamp is questionable come from battery-powered devices. As for mains hum, portable devices pick up so many hums from so many sources that i doubt much useful mains hum is ever recorded.

• by gorkish on 10/10/22, 4:45 PM

  I've heard this fairy tale for decades, and quite frankly, I'm putting it into the same camp as claims of undeleting data from magnetic media or reading license plates from space --- By that I mean that such things may be theoretically possible, but from a pragmatic and practical perspective, they might as well be complete science fiction.

  Please, can anyone find a single concrete example of ENF working? All the information I can find about the UK's supposed widespread and automated use of it starts to evaporate into the same kind of conjectural nonsense as polygraph tests.

• by nickdothutton on 10/9/22, 11:19 PM

  I have occasionally wondered if the earths magnetic field signature, which is present in solidified rock, could be read from a magnetic tape on which something has been recorded. Never had the analogue skills needed to investigate.

• by rtanks on 10/9/22, 2:38 PM

  The sound is very aggravating.

• by braingenious on 10/9/22, 10:39 PM

  This is fascinating. Does anyone know if this phenomenon is unique to Britain? I wonder if this could be replicated in other countries.

• by spoonjim on 10/9/22, 2:46 PM

  Seems like you wouldn’t need to actually record and store the mains hum… you could just extract it from other videos with known datestamps.

• by hammock on 10/10/22, 1:12 AM

  Would be interesting to generalize this technique to surmise (independently) the location of, e.g. the Osama bin Laden videos.

• by chaosprint on 10/9/22, 8:40 PM

  Interesting topic.

  I tried to mimic that sound design using Glicol but winded up getting something different.

  For those who are interested:

  1. go to (https://glicol.org)

  2. run the following code:

  // ----------------

  o: sin ~freq >> mul 0.5;

  ~freq: sin 0.2 >> mul ~range >> add 50;

  ~range: sin 0.4 >> mul 1 >> add 2;

  // ----------------

  3. tweak the numbers to get different sound

• by yarg on 10/10/22, 1:04 AM

  That's a really fat side-channel if you can extract it with minimal noise.

  You should be able to extract time and also location based up the waveform.

  And I think that it should also be possible to use baseline expectations for known channels to reduce the noise of the extract.

• by mcv on 10/10/22, 1:38 PM

  Super interesting. I notice that this is only about the UK, but I assume the same principle should work in every country, right? Are there any similar projects doing this for other countries?

• by etaioinshrdlu on 10/9/22, 6:53 PM

  I have never heard mains hum as wobbly as on this site. It seems exaggerated.

• by kzrdude on 10/9/22, 7:23 PM

  Just curious, are there any software hacks (not audio/video at all) that use any aspect of mains hum for say info leakage? (Could be impossible.)

• by nuc1e0n on 10/10/22, 12:50 PM

  This is brilliant. Anything that helps to disambiguate the authenic from the inauthentic is most welcome from my perspective.

• by shadowofneptune on 10/10/22, 8:25 AM

  Interesting how foreign this sounds to me, but how familiar it is to millions. 60 Hz must sound the same way to Britons.

• by paulkrush on 10/9/22, 3:10 PM

  Fun fact: You can hear the harmonics of the grid and IP switching if you open the site in two separate browser windows.

• by rajasimon on 10/9/22, 4:08 PM

  I bet there was a movie or a documentary around this if anyone have the link please share it.

• by MockObject on 10/10/22, 6:57 PM

  How can the whole nation's grid have the same variations everywhere?

• by eskaytwo on 10/10/22, 6:48 AM

  Has anyone tied this technique into deepfake analysis/synthesis?

• by atoav on 10/9/22, 2:39 PM

  Time to get your own isolated grid huh? Maybe with solar and inverters?

• by manv1 on 10/9/22, 5:08 PM

  This is so fucking cool.

• by 29athrowaway on 10/10/22, 1:00 AM

  You may also like to read about:

  - Yellow dots in printers.

  - Eurion constellation.

  - EXIF

• by gugagore on 10/9/22, 4:53 PM

  What I don't understand is how much technique assumes of the local oscillators on the recording device, which also vary.

• by JohnJamesRambo on 10/9/22, 2:42 PM

  This is absolutely fascinating.

• by barbazoo on 10/9/22, 4:40 PM

  It's super shitty to just autoplay that sounds as soon as you open the page. Firefox on Android.

• by sholladay on 10/9/22, 5:48 PM

  Yet another reason that the world’s electric grids should be replaced with DC power.

  AC power was only a good idea when we didn’t know how to make good DC-to-DC voltage converters.

  https://www.electricaltechnology.org/2020/06/advantages-of-h...