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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.'"
There is never a meteor when it's not fun to Law.
will eat those frequency away, or make them lose any useful phase information.
Deja vu:
http://science.slashdot.org/story/12/12/12/1331243/engineers-use-electrical-hum-to-fight-crime
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.
...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.
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. ?
Filter out 50hx or 60hz depending on your location. Thanks for the tip
Are all those people recording with a device without electrical wire affected? I don't think so.
This one didn't even make it 24 hours before it was duped.
Not even Slashdot Editors read Slashdot anymore.
But DOES IT RUN LINUX? desuka?
BSD ha shindeimasuyo!
Slashdot is lame and won't let me type Japanese.
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...
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??
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!!!
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
My security clearance is so high I have to kill myself if I remember I have it...
Run Too Fast?
Nah, Read The Fucker...
Tomorrow is another day...
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.
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!
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.
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 ?
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.
Say out loud: I'm an Aspie and I'm somewhat proud, I guess. Uh. Can I write an email in all caps instead? Hm...
Sounds just as reliable as bullet lead analysis!
http://slashdot.org/firehose.pl?op=view&type=submission&id=2399209
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.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
yep, this
Recognise The Frequencies ...
ehh, who am I kidding, of course that was typo in the most important letter combionation in slashdot.
Release the Ferrets!
This space available.
The battery is irrelevant. The EM radiation is picked up by portable devices as well, and variances are recorded.
... 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...
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
- Jesper
My security clearance is so high I have to kill myself if I remember I have it...
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.
... :-S
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
- Jesper
My security clearance is so high I have to kill myself if I remember I have it...
Hum. Bugged.
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 !!!
The only thing that would pick up the hum is a microphone. So what kind of digital recordings are these idiots talking about?
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?
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.
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.
Round the Fibonacci!
You are entitled to your own opinions, not your own facts.
Rewind The Film!!!
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...
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.
"We receive as friendly that which agrees with, we resist with dislike that which opposes us" - Faraday
can you say post-record overdub?
Record this fridge?
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?
Anyone that releases audio files where anonymity is important should be passing them through a high pass filter (and probably a low pass one) to remove potentially identifying sounds. For those curious, Audacity provides such functionality...
It's not digital recording that can be identified, it's analogue sources; and (according to recent /. article) it's not UK police who have recorded seven years of AC hum, but a UK propeller-head. But if you have access to that nerd's recordings, you can identify where an analogue source was recorded (regardless of analogue or digital recording) so long as it was recorded in the last seven years and within AC hum of one of the places that the nerd monitored.
It is quite clever; pity the article wasn't.
Newall
Perhaps we can use the electrical hum of Slashdot's servers to detect when this story was first posted.
I'm a good cook. I'm a fantastic eater. - Steven Brust
Resist the futile!
Your brain is not a computer.
I swear I saw this on NCIS or CSI at least 5 years ago. It was a plot twist that they used the technique to find out that the video recording was a fake. Sure the writers may have pulled it out of their ass at the time but it seemed plausible then.
These comments are my own and do not necessarily reflect the views or opinions of my employer or colleagues...
Not just a time but a place too. One has to imagine that something so easy and cheap (even the police could hardly be paying more than $100k each for the $100 worth of equipment it would take to log this) that it will catch on everywhere.... so perhaps you can even change the detected location of a video
Other interesting activities....
Generate a random hum into a device at capture time.
Generate a pre-recorded hum into a device at capture time.
So since the slashdot article the other day about this, how many private individuals have started data logging their power signal?
"I opened my eyes, and everything went dark again"
This may work, until some mal-do-well filters out the hum and adds back the hum from a different time-base. With good digital editing tools, this should not be impossible (difficult, but when has the merely difficult stopped anyone sufficiently motivated?).
You mean you didn't already read it when Unknown Lamer posted it on Wednesday?
Random Text Fuckup!
Release The Fogs
--Mr Durns
Tomorrow is another day...
IN HERE
In Here
in here
in here... ere... ere..
We already demolished this story on Wednesday, when it was posted as a "terrist fool proofer".
"Flyin' in just a sweet place,
Never been known to fail..."
Release The Fraken!
Astronomers have been using the "Universal" grid to look backwards in time at "signatures" bouncing off interstellar clouds of supernova that occurred 800 or more years ago.
It seems even interstellar dust particles reflect some light from an object and all you have to do to reconstruct the 'scene of the crime' is to collect the light and piece it back together.
This is very similar, every event in Time occurs concurrent with other events that go on all the time. If you have a recording of one event you necessarily recorded more than you thought you would. In essence.. quantum entanglement doesn't drift, it entangles more and more.. what's odd about the study of entanglement is we try to monopole it to understand it.. constrain it to one direction.
Same oddity here, looking for a road map to a Time signature by looking for a known signal previously recorded as a reference.
Sherlock Holmes often did the same thing with 'deduction' not 'inference'.. although Einstein might beg to differ. Inference is a faith or trust that a system is understood well enough to anticipate without evidence. It is a blind adherence to physical laws.. which sometimes fall short. Deduction looks at the interconnectedness of things as 'they are' and makes corrections.. no matter how unlikely they appear.. to resolve the final outcome and learn from it.. as the basis of future projections.
So current quantum entanglement studies are an exercise is isolation, experimental oddity.. and may eventually lead to inference, but are fundamentally deductive.
A more impressive system would use multiple signals co-mingled to 'bring' the information to the listener. Somewhat like a steering a sonar array. Without instrumentation. It might appear more like magic, but current quantum entangled comptuer studies are headed in that direction.. if you blend enough signals together and steer them right, the desired signal should arise from the noise.. rather like a Fourier transform mimicks any desired signal if you process it enough.
Repeat This Frequently
For every benefit you receive a tax is levied. - Ralph Waldo Emerson
Wow, they just created a black market for low quality recordings of silence. Finally found a use for an intentional ground loop.
easy: :)
1. edit recording all you want
2. notch filter out mains hum so its real quiet (almost gone)
3. add in mains hum from silence recording you purchased from me for top dollar
I have teeth marks on my eyelids!
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
This is very futuristic and smart
battery power & filter out 50hz, 100hz & 3rd harmonic .. ...
not that many formats record low level signals without extreme degredation, phase distortion or quality, if at all.
something's not right here
The entire grid is synchronized. It's one of the more important applications of highly accurate timekeeping.
As the article notes, there's drift - but that's precisely what helps make the pattern unique.
In the US, we have lots of independent suppliers and networks. A recent outage on the east coast affected all of Cambridge, but none of the surrounding towns because of the peculiarities of power distribution.
Please help metamoderate.
Nearly every modern cell phone has active noise reduction in it's A2D/D2A DSP. In addition to that more modern phones have second layer reduction within software. Constant noise, such as 50Hz hum is something that you would explicitly target to remove, as it costs more money (bandwidth) to send that noise down the line, and reduces call clarity.
The only way I see this really working is if it's an untouched recording (vinyl, land line with no active filtering, ultra-clean DSP into digital, etc).
That said, it's interesting..
It should be possible to analyze the signal in recordings of verified dates older than seven years to reverse engineer a historic log British power consumption.
Anybody who has designed any good digital equipment that has an analog front-end knows that you end-up putting 50 and 60 Hz filters in specifically to avoid vacuuming-up all the stray 50 and 60 Hz noise in the Environment from AC power lines (50Hz primarily for Euro, and 60Hz primarily for US). Any artifacts of mains noise that made it through would then be further trashed by lossy compression (which has become prevalent in consumer audio devices). I strongly suspect this is in the family of "scientific breakthroughs" that has no purpose or value ... except in "expert witness" testimony designed to mislead gullible, technologically-challenged jurors in court cases.