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Electrical Grid Hum Used To Time Locate Any Digital Recording

samzenpus posted about a year and a half ago | from the can-you-hear-that dept.

United Kingdom 168

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.'"

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168 comments

O_o (-1, Redundant)

Markizs (674865) | about a year and a half ago | (#42284857)

That does sound quite awesome. Maybe I will even RTF!

Re:O_o (-1)

Anonymous Coward | about a year and a half ago | (#42285039)

Rich Text Format?

Re:O_o (0)

Anonymous Coward | about a year and a half ago | (#42285059)

Run Too Fast?

Re:O_o (4, Informative)

gagol (583737) | about a year and a half ago | (#42285065)

Nah, Read The Fucker...

Re:O_o (1)

Markizs (674865) | about a year and a half ago | (#42285235)

Recognise The Frequencies ... ehh, who am I kidding, of course that was typo in the most important letter combionation in slashdot.

Re:O_o (4, Funny)

Jafafa Hots (580169) | about a year and a half ago | (#42285257)

Release the Ferrets!

Re:O_o (1)

Cwix (1671282) | about a year and a half ago | (#42285495)

Round the Fibonacci!

Re:O_o (1)

Anonymous Coward | about a year and a half ago | (#42285561)

Rewind The Film!!!

Re:O_o (1)

goldaryn (834427) | about a year and a half ago | (#42285885)

Record this fridge?

Re:O_o (1)

Markizs (674865) | about a year and a half ago | (#42285229)

yep, this

Re:O_o (2)

Zemran (3101) | about a year and a half ago | (#42285437)

Release this fart...

Electrical Grid (0)

Anonymous Coward | about a year and a half ago | (#42284861)

There is never a meteor when it's not fun to Law.

Audio compression (0)

Anonymous Coward | about a year and a half ago | (#42284865)

will eat those frequency away, or make them lose any useful phase information.

Re:Audio compression (0, Flamebait)

wonkey_monkey (2592601) | about a year and a half ago | (#42284919)

Thanks professor! You are a professor, aren't you? I mean, you wouldn't come here expressing something as scientific fact when you had no experience in the field whatsoever, would you?

Re:Audio compression (5, Funny)

dwywit (1109409) | about a year and a half ago | (#42285485)

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!

Re:Audio compression (2)

gl4ss (559668) | about a year and a half ago | (#42285817)

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

Re:Audio compression (0)

Anonymous Coward | about a year and a half ago | (#42285187)

and lo, god said, behold ye my mighty lossless compression algorithm!

Re:Audio compression (2)

flyneye (84093) | about a year and a half ago | (#42285571)

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.

Dupe (5, Informative)

Patch86 (1465427) | about a year and a half ago | (#42284867)

Re:Dupe (5, Funny)

Anonymous Coward | about a year and a half ago | (#42284897)

If only they could apply their amazing technology to matching slashdot articles against ones that have already been posted in the last 7 years.

Dope maybe (1)

Anonymous Coward | about a year and a half ago | (#42284923)

This one didn't even make it 24 hours before it was duped.

Not even Slashdot Editors read Slashdot anymore.

But it's leading edge tech! (4, Funny)

Anonymous Coward | about a year and a half ago | (#42285087)

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!

Re:But it's leading edge tech! (1)

dwywit (1109409) | about a year and a half ago | (#42285503)

Kind of how the funniest joke in the world was translated into German - if the mods see more than two words together, they'll be hospitalised.

Re:Dupe (1)

nospam007 (722110) | about a year and a half ago | (#42285393)

"If only they could apply their amazing technology to matching slashdot articles against ones that have already been posted in the last 7 years."

Damn, I so wanted to market my brad-new humcrypting technology.

Re:Dupe (1)

Zemran (3101) | about a year and a half ago | (#42285459)

If only they could apply their amazing technology to matching slashdot posts against ones that have already been posted in the last 7 minutes.

Still sceptical (0)

Anonymous Coward | about a year and a half ago | (#42284869)

This is a dupe, but I didn't mention last time I'm a bit sceptical on how useful this is. For starters, recordings that are going to be used for evidence in court may well be made with off-the-grid recording equipment (pocket recorder, smartphone). Second, if the recording was made on the grid, location dependent (data for the grid in London is useless if the recording was made elsewhere). Third, to save space, audio is frequently converted to some lossy, psychoacoustically modelled version of the original such as mp3. If you can't hear it, it's filtered out, ultimately leaving you with humless recordings.

Re:Still sceptical (5, Insightful)

Fleetie (603229) | about a year and a half ago | (#42284931)

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.

Re:Still sceptical (2, Informative)

Anonymous Coward | about a year and a half ago | (#42285003)

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.

Re:Still sceptical (5, Interesting)

Ford Prefect (8777) | about a year and a half ago | (#42285029)

At the utterly fascinating Georgetown Steam Plant Museum [flickr.com] 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 [wikipedia.org] , 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.

Re:Still sceptical (1)

dwywit (1109409) | about a year and a half ago | (#42285525)

Yes, it's tricky, and the local generators/distributors where I live (South-east Qld, Australia) are starting to become worried about the amount of grid-connected solar systems. Still, you cannot connect your solar PV to the grid without approved inverters, which not only match phase, but also disconnect whenever the grid has an outage.
br.Lucky I'm off-grid - the energy from my smug grin keeps the batteries topped up when the weather's lousy.........

Re:Still sceptical (0)

Anonymous Coward | about a year and a half ago | (#42285341)

I use 60Hz you insensitive clod!

Re:Still sceptical (1)

mSparks43 (757109) | about a year and a half ago | (#42285369)

Not sure about this, (not seen the post you are replying to), but the frequencies will vary a lot by location, the fact it is not "fixed" is how they are identifying the time, it may be "locked" but that does not necessarily mean that the variations from what they are supposed to be "locked to" will not vary widely across the country.

Re:Still sceptical (0)

Anonymous Coward | about a year and a half ago | (#42285599)

Actually locked to is exactly what this means for an electricity net. If the phase of a power generator is off then it would cause a short-circuit of sorts and power is wasted as heat.

Re:Still sceptical (3, Informative)

Anonymous Coward | about a year and a half ago | (#42285553)

You can see the current state of the UK power generation network dynamically here:

http://www.dynamicdemand.co.uk/grid.htm [dynamicdemand.co.uk]

Re:Still sceptical (0)

Anonymous Coward | about a year and a half ago | (#42285625)

I remember someone did research on human humming, when you ask someone to simply hum (no song or anything, just on the 'fundamental' tone of that person) it seems that people who live in a 60Hz country have a higher pitch than people who live in a 50Hz country.

Re:Still sceptical (0)

Anonymous Coward | about a year and a half ago | (#42285741)

if the recording was made on the grid, location dependent (data for the grid in London is useless if the recording was made elsewhere).

Re: Location: Wrong.

So you are saying that you can use this London data to time stamp a recording made in Afghanistan or Singapore? I think you are the one who is wrong.

Re:Still sceptical (4, Insightful)

StoneyMahoney (1488261) | about a year and a half ago | (#42285041)

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.

Re:Still sceptical (3, Interesting)

HungryHobo (1314109) | about a year and a half ago | (#42285225)

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.

Re:Still sceptical (1)

lucmove (757341) | about a year and a half ago | (#42285735)

If the police can record the hum, so can human beings.

You underestimate the technology and prowess of the extraterrestial police.

An Article About a Clever British... (5, Funny)

lourd_baltimore (856467) | about a year and a half ago | (#42284871)

...application of technology and not one utterance of "boffin"??!?!?
I demand satisfaction!

Re:An Article About a Clever British... (1)

Anonymous Coward | about a year and a half ago | (#42285035)

It's a beeb article, not a Reg one.

Re:An Article About a Clever British... (0)

Anonymous Coward | about a year and a half ago | (#42285795)

It's a beeb article, not a Reg one.

The article is about Justin Bieber? Thankfully, I did not RTFA in keeping with the /. modus operandi. ;)

Re:An Article About a Clever British... (1)

Bitsy Boffin (110334) | about a year and a half ago | (#42285055)

Never fear, it is I, the bitsy boffin, to your rescue!

Boffin's unite!

Re:An Article About a Clever British... (0)

Anonymous Coward | about a year and a half ago | (#42285521)

Many boffin's died . . . to bring us this information.

Re:An Article About a Clever British... (1)

girlintraining (1395911) | about a year and a half ago | (#42285933)

...application of technology and not one utterance of "boffin"??!?!? I demand satisfaction!

You're from Cardiff, aren't you?

This could get messy (1)

whoisisis (1225718) | about a year and a half ago | (#42284883)

So now what the bad guys have to to after tampering with audio recordings is to subtract the hum of the mains and add the hum at a different time. ?

Re:This could get messy (0)

Anonymous Coward | about a year and a half ago | (#42285115)

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?

Re:This could get messy (2)

gl4ss (559668) | about a year and a half ago | (#42285857)

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?

Re:This could get messy (0)

Anonymous Coward | about a year and a half ago | (#42285127)

That is not the point.

In a similar way, "light" is used to identify thieves. Now you are saying: "What if the thieves use a mask? Let's stop using light as a means to identify thieves!"

Re:This could get messy (1)

Anonymous Coward | about a year and a half ago | (#42285509)

The biggest thieves are identified by something called a vote.

Re:This could get messy (1)

Dot.Com.CEO (624226) | about a year and a half ago | (#42285747)

This makes no god damn sense.

Re:This could get messy (0)

Anonymous Coward | about a year and a half ago | (#42285881)

He's talking about politicians...pretty obvious if you ask me.

Filter (0)

Anonymous Coward | about a year and a half ago | (#42284899)

Filter out 50hx or 60hz depending on your location. Thanks for the tip

Re:Filter (1)

dwywit (1109409) | about a year and a half ago | (#42285563)

And that won't leave a suspicious notch or gap in your recording - sure, it's removed the police's "timestamp", as it were, but it raises their suspicion level, and gives them a bit more motivation to spend more time and effort focussed on your activities.
 
Why not find some other 50 or 60 cycle hum to substitute instead?

Re:Filter (1)

gl4ss (559668) | about a year and a half ago | (#42285871)

I wouldn't say it to raise suspicion level by any meaningful degree. and they'd already have the recording then and if they're tapping you live they know when it's recorded..

the reason why it wouldn't raise suspicion level is that if you're going to do any kind of decent job at doing an audio recorder you want to get rid of that constant anyhow.

who needs an electrical wire anyway (0)

Anonymous Coward | about a year and a half ago | (#42284907)

Are all those people recording with a device without electrical wire affected? I don't think so.

Linux (0)

Anonymous Coward | about a year and a half ago | (#42284929)

But DOES IT RUN LINUX? desuka?

BSD ha shindeimasuyo!

Slashdot is lame and won't let me type Japanese.

Great... (1)

Delgul (515042) | about a year and a half ago | (#42284949)

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...

Re:Great... (1)

bipbop (1144919) | about a year and a half ago | (#42284965)

More like notches on the fundamental and harmonics as necessary.

Re:Great... (2)

TheGratefulNet (143330) | about a year and a half ago | (#42284967)

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)

Re:Great... (1)

gweihir (88907) | about a year and a half ago | (#42285397)

This is only partial BS. Much forensic evidence is not worth a lot more. For example, fingerprints are easy to fake.

Re:Great... (1)

Anonymous Coward | about a year and a half ago | (#42284975)

It's used to validate authenticity of recordings. If the material is possibly tampered with they would check the hum to try to get additional confirmation to decide wether it might be sable as evidence in court. No hum could be a sign that it was manipulated and should not be used.

Re:Great... (2, Informative)

Anonymous Coward | about a year and a half ago | (#42285063)

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.

Re:Great... (4, Insightful)

locofungus (179280) | about a year and a half ago | (#42285489)

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.

Not creepy behaviour AT ALL! (1)

chris.alex.thomas (1718644) | about a year and a half ago | (#42284953)

I mean, who wouldnt want to record londons electrical power signatures..Sounds like the first thing I'd want to do when I got home....o.O.....seriously??

Re:Not creepy behaviour AT ALL! (1)

azalin (67640) | about a year and a half ago | (#42284981)

Looking back onto their actions, recording the background hum for 7 years is only slightly creepy. They can do worse.

Re:Not creepy behaviour AT ALL! (1)

gagol (583737) | about a year and a half ago | (#42285227)

Some people buys recordings of silences from the BBC... so my guess is this is normal behaviour based on english standards.

Cool... Time for a crime spree!!! (0)

Anonymous Coward | about a year and a half ago | (#42284961)

Cool... now I'll just film myself on my couch in the living room watching a video on my ipad, then just dub in a white noise recording I set up in my living room while I'm actually out on a crime spree!!!

Won't distributed power transformers change it? (1)

SplatMan_DK (1035528) | about a year and a half ago | (#42285045)

I am not an Electrical Engineer (hmmmm, "IANAEE"?) but won't the captured frequency variations be changed by de-centralized power transformers?

A normal power-grid is full of distributed power transformers which change the voltage for different needs during the distribution net. They come in vrious sizes ranging from large transformer-stations to the small local power transformer down the block from your home. Won't all these big transformers even out the slight changes in frequency?

And what happens with an area being served with power from a different powerplant? Won't that have a completely diferent signature?

I read TFA but it was extremely thin on the technical details.

- Jesper

Re:Won't distributed power transformers change it? (2)

u38cg (607297) | about a year and a half ago | (#42285085)

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).

Re:Won't distributed power transformers change it? (1)

Shimbo (100005) | about a year and a half ago | (#42285233)

A double conversion UPS would do the job.

Re:Won't distributed power transformers change it? (0)

Anonymous Coward | about a year and a half ago | (#42285647)

Not really. While the ripple voltage between the two converter steps will be modulated with the 50/60Hz power. The first conversion step will charge the battery during peaks and the battery voltage ripple will have the same frequency as the rectified input power. This ripple is lower than it would be on a single conversion step but it will still be there.
What you can do is to use dual batteries and switch which one to charge/use but you will still get EM noise from the grid at the mentioned frequencies. (The method mentioned probably works on portable devices too.)

The safe thing to do is to do the recording either in a completely shielded room like a measurement lab or way off from civilization like out on the ocean or something.

Re:Won't distributed power transformers change it? (0)

Anonymous Coward | about a year and a half ago | (#42285141)

What I don't understand is, how is a battery powered camera affected by the noise on the powerline? If it is EM radiation from the powerlines in the walls, I don't see how it is possible to filter this out of all the other noise in the area from microwaves, bad power supplies, motors, compressors...

If it is from the power line direct through the power adapter, then wouldn't a decent workaround be "use only battery powered recording devices"?

Batteries are irrelevant (1)

SplatMan_DK (1035528) | about a year and a half ago | (#42285313)

The battery is irrelevant. The EM radiation is picked up by portable devices as well, and variances are recorded.

The sound signature is generated by the ambient frequency variance generated by the power grid EMR. And while you are correct that local noise may disrupt it, odds are there will be plenty of timeslots in a recording where no noise is present - or where the extra noise can be filtered.

I find the whole idea pretty elegant. The only way to get by this is probably to actively filter the involved frequency ranges in the recording.

And then offcourse there is the problem of fraud ... it wouldn't be too hard for intelligent criminals (ok, wait, i see a problem allready ...) to fake this by falsifying the noise in a recording. Simply swapping recorded noise from a different time may be sufficient to fool investigators...

- Jesper

Re:Won't distributed power transformers change it? (2)

gweihir (88907) | about a year and a half ago | (#42285403)

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.

Re:Won't distributed power transformers change it? (0)

Anonymous Coward | about a year and a half ago | (#42285771)

Expensive? Just get a cheap 12V PSU and inverter (The ones designed to run off a cigar lighter socket)

How hard would it be to actually do this yourself? (1)

tamyrlin (51) | about a year and a half ago | (#42285079)

This is a really cool application. I wonder how hard it would be to write an application to do this yourself as a way of identifying for example when a certain TV broadcast was recorded.

Also, for those of you who are interested in what the phase noise looks like there is a nice article about this over at leapsecond.net: http://www.leapsecond.com/pages/mains/ where the phase noise of the power grid is compared to a GPS clock.

Re:How hard would it be to actually do this yourse (3, Insightful)

MancunianMaskMan (701642) | about a year and a half ago | (#42285117)

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!

Clean your feed, Slashdot (2)

Anonymous Coward | about a year and a half ago | (#42285113)

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.

could they have used this on osama? (1)

hibji (966961) | about a year and a half ago | (#42285131)

Would be interesting if they tried this technique to find osama. The guy put out some videos at some point and im assuming they weren't all from a cave.

Battery powered equipment ? (0)

Anonymous Coward | about a year and a half ago | (#42285165)

how about, if you make/mix/edit a recording with battery powered equipment only ?
will that still pick up a hum (from RFI emmitted from the nearest wiring) even when not plugged in ?

Is that so hard to fake? (1)

Dr. Hok (702268) | about a year and a half ago | (#42285167)

What if you run the audio through a 50 Hz (60Hz in America) band reject filter and then add some hum from another time? Then the recording has a different time fingerprint.

Re:Is that so hard to fake? (2)

Kergan (780543) | about a year and a half ago | (#42285199)

TFA notes that sound engineers have trouble getting rid of it. Else, agreed... filter, add a different hum; can't be that hard...

True - and who has the resources for that? (1)

SplatMan_DK (1035528) | about a year and a half ago | (#42285327)

What if you run the audio through a 50 Hz (60Hz in America) band reject filter and then add some hum from another time? Then the recording has a different time fingerprint.

Agreed.

The potential for fraud is a troubling thought. And while intelligent criminals (hmmm, ok, I see the problem allready) may be able to do this, odds are the only real player with the resources to do fraud in this area are the authorities themselves - which is actually grounds for real concern ... :-S

- Jesper

Re:Is that so hard to fake? (2)

gweihir (88907) | about a year and a half ago | (#42285425)

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.

Oh good! More unproven crap becomes "evidence". (0)

Anonymous Coward | about a year and a half ago | (#42285171)

Sounds just as reliable as bullet lead analysis!

Easy to fake no (1)

gweihir (88907) | about a year and a half ago | (#42285223)

Now that this has been documented, any halfway competent audio or electronics engineer should be able to fake this. Before, it required a bit more skill, but was still easy to do.

The only remaining application is if integrity of the audio is ensured, but not its time-stamp. That situation must be exceedingly rare.

Bah. (0)

Anonymous Coward | about a year and a half ago | (#42285339)

Hum. Bugged.

Stop Piracy ? i think NOT ! (0)

Anonymous Coward | about a year and a half ago | (#42285351)

Its not April 1st is it ? What a load of rubbish ! The UK mains does vary 49-51 and the dips are made up by running some stations higher(faster) , (DRAX is one) but all uk is "tied" together and even if regions were supplied by local power stations (which they are NOT) this would only enable "BIG BROTHER" to track on a city level , BTW I regularly use a scope to monitor mains volatge & Frequancy , not related to snooping though , Keep on pirating !!!

Re:Stop Piracy ? i think NOT ! (1)

Jarik C-Bol (894741) | about a year and a half ago | (#42285565)

its for locating events temporally, not geographically. Did you read the summary or not?

Huh? (0)

Anonymous Coward | about a year and a half ago | (#42285399)

The only thing that would pick up the hum is a microphone. So what kind of digital recordings are these idiots talking about?

Batteries (1)

benwad (1979558) | about a year and a half ago | (#42285421)

The first example they used in the article is a covert recording, and I assume this means on a portable device. I know very little about electricity but surely the frequency of the national grid has no effect on recordings made on battery-powered devices?

batteries??? (0)

Anonymous Coward | about a year and a half ago | (#42285443)

Wow, any recording huh?
What about devices running on batteries?
What about microphones that have 50/60 hz notch filters (for reducing the hum).

Duh.

Re:batteries??? (1)

Chrisq (894406) | about a year and a half ago | (#42285921)

Wow, any recording huh? What about devices running on batteries? What about microphones that have 50/60 hz notch filters (for reducing the hum).

Duh.

I would think that most equipment with exception of real top end equipment or something running in a Faraday cage would have some measurable hum

UPS Work-Around (0)

Anonymous Coward | about a year and a half ago | (#42285573)

This seems a bit bogus to me. For one thing... the components in your PC operate on a DC signal from one of the voltage rails from your PC's PSU. Granted, the DC signal is generated via the equivalent of a rectifier circuit, so in theory there may be some measurable trace, but a modern PC PSU also includes all sorts of smoothing capacitors and circuitry designed specifically to iron out the very wrinkles this article claim will fingerprint a recording. It's necessary to do this because the voltages and currents used by PCs clocked at gigahertz would otherwise be vulnerable to even miniscule variations in that supply...

But let's suppose that the story is true...

What if you had a decent-quality in-line UPS between your recording device and the mains? Essentially, that will take mains electricity, store it in a battery, then on the "close" side of the battery - on your PC - it will use an inverter to restore a 50Hz Alternating Current. If you use that, then the frequency that gets mapped to your recording would be from your inverter, not the external supply.

What if your house is fitted with home generation [photo-voltaic cells] and a 2-way electricity meter? That means you've got another inverter in the circuit, providing yet another clock signal.

Or what if, like my home, you've got a 15-year-old but entirely servicable refridgerator, that spikes the crap out of the local ring mains each time it starts it's compressor? I have to run a section of Ethernet-Over-Mains between two parts of my home that are too well shielded for a decent wireless signal, and until I put an isolator on it, the fridge was a nightmare...

Bottom line, I suspect there are just too many variables to make this a believable story...

Random number alternative (1)

davide marney (231845) | about a year and a half ago | (#42285629)

If the signal fluctuations are truly unique and unpredictable over time, maybe a web service that returns a signature on request would be a good alternative to a random number generator which is sometimes not so random.

photoshopping (0)

Anonymous Coward | about a year and a half ago | (#42285699)

can you say post-record overdub?

Nobody can fake a tape - except the Met Police (2)

Chrisq (894406) | about a year and a half ago | (#42285905)

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 [independent.co.uk] tamper [hostingprod.com] with evidence [bbc.co.uk] . Would they?
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