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Electrical Grid Hum Used To Time Locate Any Digital Recording
illtud writes "It appears that the Metropolitan Police in London have been recording the frequency of the mains supply for the past 7 years. With this, they claim to be able to pick up the hum from any digital recording and tell when the recording was made. From the article: 'Comparing the unique pattern of the frequencies on an audio recording with a database that has been logging these changes for 24 hours a day, 365 days a year provides a digital watermark: a date and time stamp on the recording.'"
Deja vu:
http://science.slashdot.org/story/12/12/12/1331243/engineers-use-electrical-hum-to-fight-crime
...application of technology and not one utterance of "boffin"??!?!?
I demand satisfaction!
http://science.slashdot.org/story/12/12/12/1331243/engineers-use-electrical-hum-to-fight-crime
systemd is Roko's Basilisk.
Re: Location: Wrong. The entire UK grid is "locked together" and it all runs at the same frequency. Necessarily. Also: Recorder doesn't need to be plugged into the mains. 50Hz hum permeates the space around us. Try grabbing hold of an oscilloscope lead and look at how much 50Hz hum you are "carrying". Unless you're a long way from mains outlets, it's a lot.
"Absorbing your worst..."
not even that. modulate the signal with noise.
done.
(seriously. this is so easy to fool. I must be missing something OR this is total BS)
--
"It is now safe to switch off your computer."
Frequency varies with the total load on the grid net. Every single generator has to be synched (phased in) to the grid and they all then run at the same frequency throughout the system. To keep frequency stable the system needs to regulate all power generators according to current demand to keep the frequency from shifting too much. The frequency is always monitored and managed so it will average out over the year to within the limits set by law.
Power generation and proper regulation is really tricky business, especially when you have lots of wind and nuclear. Water dam generators are good for quick compensation though. Homeowners with private solar and wind connected to the grid, not so much.
At the utterly fascinating Georgetown Steam Plant Museum in Seattle, I learned of the difficulties in getting a (somewhat elderly) generator in sync with the grid. Apparently, get it right and all the other power stations will pull it into the exact frequency - get it wrong, and you'd snap the turbine shaft.
As for the mains hum, in an undergraduate experiment at Jodrell Bank Radio Observatory, I detected intelligent life - on Earth, unfortunately. While running an FFT on a recording of a pulsar, we not only uncovered the spinning neutron star's rotation - we also discovered some not-exactly-mysterious peaks at multiples of 50Hz.
Tedious Bloggy Stuff - hooray?
You can hear 50hz. It won't be stripped out, although it's such a low volume noise you'll need some funky recovery algorithms to pick it out - oh look, those have been around for a while now. I'd be interested to hear exactly how accurately they can pinpoint the time and date. Are we talking to within a few hours, or are there sufficiently frequent irregular fluctuations you can do pattern matching to pin it down precisely to the second?
I do have my doubts over how resiliant this technique would be to forgery. If the police can record the hum, so can human beings. Say you wanted to have a conversation with someone verified by police as taking place after it really did. You record the conversation, use live hum data to cancel it out without damaging the audio, then a week later you record and mix in some fresh live hum noise. Can't see any decent sound engineer with the right equipment having any trouble with that, I know a guy who'd have a whale of time with it, and there goes any hope of this evidence ever standing up in court.
Now every terrorist knows that they need to apply a simple high-pass filter to their recording before releasing it... I would have kept this from the public if I were the police, but hey... that's just me...
According to the article the technique has been used as Prosecution evidence in court. I think that means they have to describe their methods otherwise they'd just be saying "We can tell this recording is genuine because of some unspecified magic that we won't be talking about." I'm not sure that would work for me if I was on the jury.
Nah, Read The Fucker...
Tomorrow is another day...
I'm not an Electrical Engineer either, but I took a class on it once. The whole grid is locked together and it's changes in load that cause the frequency variations. The transformers have no effect on frequency (presumably a second order fixed effect, but that's irrelevant).
[FUCK BETA]
You're not giving them due credit for their pioneering use of amazing new load-balanced submissions technology, in which each word of a post is sent to a different editor for review.
Sure, they still have a few niggles to sort out, but man, this is the future!
Quit putting animated gif ads in your feed or I'll unsubscribe. I primarily read on my mobile and downloading these big, useless images is a drag.
Now here's an idea for an even cooler application: A web service which allows customers to upload any edited audio recording and I can apply a subtle hum with a user-selected timestamp so it authenticates as "not edited original recording" with the Met Police's database! I shall start recording the mains hum shortly. Criminals rejoice! Huahahahahaha!
TFA notes that sound engineers have trouble getting rid of it. Else, agreed... filter, add a different hum; can't be that hard...
well. some people can hear it.
back when I was in uni the multimedia lecturer was playing tones at different frequencies. "oh, and any of you who've spent too long in the computer lab won't be able to hear this" most of us were stone deaf in a small range around the frequencies put out by electrical equipment.
Release the Ferrets!
This space available.
Transformers do not change frequencies. There are possibilities to do it though, but they are expensive. Also, DC transmission lines completely decouple source and destination grids, but they are still rare.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
Removing the original is exceedingly different, because of harmonics. But you could just add hum from, say, 100'000 other times. Or you can add noise that is louder than the hum. Just add stuff to it until the fingerprint-filter does not give any useful signal anymore.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
Release this fart...
I love stacking my barbecues in the shed at the end of summer - you can't beat a bit of grill on grill action.
Well, I'm sure that the 50Hz hum sounds much warmer in its original format without digital sampling errors and whaarrrgarrbbll bitrate rhubarb rhubarb harmonics frequency blah-diddy blah blah blah oxygen-enhanced one-way digital cables, so there!
They sentenced me to twenty years of boredom
As with so many of these forensic tests, what this test can unambiguously be used for is to prove that a recording _HAS_ been tampered with.
If there is no hum, or it appears to be correct then the most you can say is "it might be a genuine recording made at the appropriate time" but if there is hum, and it's obviously discontinuous then you can categorically state that the recording has been tampered with.
Unfortunately, most people, including prosecutors, defence, juries, judges, politicians etc, do not understand the distinction. There are two possible answers to "has this recording been tampered with:" YES and I DON'T KNOW. People like certainty so this gets changed to YES and NO and while in most cases that NO does turn out to be correct, you get miscarriages of justice when it's not the case.
Tim.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
You can see the current state of the UK power generation network dynamically here:
http://www.dynamicdemand.co.uk/grid.htm
Personally, I keep a sample of hum in my studio to run back against the recording to remove the hum from my digital recordings.
Those English cops can keep on working on perfecting the "hum" job.
*Repent!Quit Your Job!Slack Off!The World Ends Tomorrow and You May Die!
I think he uses the phone every now and then. so, he'd have experience.
the other article I read about this hum was more realistic and meaningful - that you could use noise to detect if a recording was altered.. since you're then comparing noise in one recording compared to noise in that very same recording. that would work on places that are behind some UPS solution too.
if it sounds too good to be true.. it probably is.
that sort of noise is _exactly_ the thing filtering done on audio signals prior to compressing is supposed to get rid of and which kind of noise encoding schemes are designed to lose the information for
world was created 5 seconds before this post as it is.
No, they have to buy what audio techs have used for years to get rid of it in professional recordings, Furman power conditioners.
I have to ask, if this is real, why does it get published?
they ran out of the initial funding, had zero applications or use cases for it and thought public support could help fund the project.
why does anything government funds for a decade in secret get published?
world was created 5 seconds before this post as it is.
Nobody can fake a tape - except the Met Police who can play back their recorded hum in a soundproof room. Of course the would never tamper with evidence. Would they?
I use 60Hz you insensitive clod!
In that case you probably are in North America.
Now they know where you are and when. Other information will be available shortly and you won't be anonymous for much longer...
I'll see your Constitution and raise you a Queen.
His name is Bob, he lives down the street from me.
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You forgot to mention the doohickey... there's always a doohickey involved.
You have the right to remain sentient. If you give up the right to remain sentient, you will be elected to public office
I do have my doubts over how resiliant this technique would be to forgery. If the police can record the hum, so can human beings. Say you wanted to have a conversation with someone verified by police as taking place after it really did. You record the conversation, use live hum data to cancel it out without damaging the audio, then a week later you record and mix in some fresh live hum noise. Can't see any decent sound engineer with the right equipment having any trouble with that, I know a guy who'd have a whale of time with it, and there goes any hope of this evidence ever standing up in court.
I am not familiar with removing noise in the audio spectrum but am in the RF spectrum. If we have a predictable noise source it can be filtered out, the problem is that when you take out the hum you will also take out some of the other noise as well, then when you put the correct hum in it's not interacting with the same noise frequencies, so you are left with nulls in the frequencies you removed the hum from which may be detectable. This eliminates putting the correct hum onto a recording made at a different time. The other method is to dub a voice onto the recording, when you record the person you will also get noise in that recording, noise that has to be eliminated as it will be out of place in the final recording. Again when you remove the noise you will be removing part of the signal that you want to keep which may be detectable. The only real way to isolate the voice from everything else is to record in a quiet room as trying to isolate the signal from the noise becomes difficult, so you would need to get the victim to cooperate. While I agree that it's not impossible to forge a recording, if the listening device is good the noise becomes too hard to forge.
Knowledge = Power
P= W/t
t=Money
Money = Work/Knowledge so the less you know the more you make
In theory, and probably in practice the frequency going through a transformer does not change. It may lead or lag slightly from one side to the other, which is basically the power factor, but other than that offset, it should be stable.
However, you got me thinking. Power factor tends to be stable, and there are devices that correct the power factor. I wonder if such a device could be modified to produce an unstable power factor, possibly driven by a pseudo-random generator. The result would be an output that seems to "move around" relative to the input. On a small scale, probably not that interested, but if done for a large building drawing megawats of power (perhaps even a data center), it might produce enough random noise +-50hz to make a recording in the area untraceable.
On a smaller scale, it would be easy to create a solar installation in the middle of nowhere that does not exhibit this property (because it is DC, not AC). Now with a battery source some simple circuits could generate 50Hz hum at an independent from the grid rate, and/or lots of similar "noise". While perhaps impossible to get far enough from the mains (in the UK anyway) that none of the actual grid would be picked up, it's probably possible to muddy the right part of the spectrum enough it can't be traced.
Maybe, for a CMOS sensor with a rolling shutter and a long enough shutter time, you could theoretically capture some time-varying EM radiation. You can see the rolling shutter causing the "jello-cam" effect on videos shot on e.g. mobile phones. But it would only be a few cycles (ten at best, the camera doesn't use a rolling shutter anymore for very long exposures), and my guess is that thermal noise is much larger.
TL;DR: NO.
for i in `facebook friends "=bday" 2>/dev/null | cut -d " " -f 3-`; do facebook wallpost $i "Happy birthday!"; done
Okay, fine, so it has a 50hz beat. But but the question is, can you dance to it?
Slightly off-topic but fun: my favorite party trick for a self-confessed audiophile -- Admire their overpriced collection of obscure amps and equipment costing more than the average suburban home. Put on a look of concern and when asked what's the matter, mutter "Lovely bit of kit, andand perhaps it's just my ears, but I think there's some muddiness in the midrange that erodes the transparency." Off they go, down the rabbit hole of knob twiddling and speaker placement for the next several hours.
Not even Slashdot Editors read Slashdot anymore.
There's multiple editors approving stories, but the real kicker is that they don't even use Slashdot's search function before posting an article. I mean, for FSM's sake people, that's why it exists!