An average person on the street may find it hard to tell the difference between an unaltered recording and one that's been edited or tampered with in some way, but forensic experts are often tasked with just that responsibility. Thankfully there's one technique that's nearly foolproof so long as the aural evidence is there. For the past several years, authorities in London have been recording a continuous log of the "mains" frequency — a slight hum (normally inaudible to human ears) that accompanies the distribution of electricity. The mains frequency provides a unique, constantly shifting sonic fingerprint that forensic specialists can match up against nearly any audio sample.
So long as a provided clip was recorded near a power...
via The Verge - All Posts http://www.theverge.com/2012/12/12/3758178/electricity-hum-electric-network-frequency
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