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.'"

Comments

Dupe

[Patch86]

Deja vu:
http://science.slashdot.org/story/12/12/12/1331243/engineers-use-electrical-hum-to-fight-crime

Re:Dupe

[Anonymous Coward]

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

An Article About a Clever British...

[lourd_baltimore]

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

Can this be used to identify dups?

[wonkey_monkey]

http://science.slashdot.org/story/12/12/12/1331243/engineers-use-electrical-hum-to-fight-crime

Re:Still sceptical

[Fleetie]

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

[Ford Prefect]

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.

Re:Audio compression

[dwywit]

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!