Electric Grid Hum Used to Time-Stamp Digital Recordings, Verify Evidence
December 14, 2012 1:07 PM
comment(s) - last by
UK police are putting tactic to use to fight crime
Romanian audio specialist
Dr. Catalan Grigoras
, now director of the National Center for Media Forensics at the
University of Colorado
, Denver, made an intriguing discovery about a decade ago. The ubiquitous hum of modern society follows a unique pattern that allows many recordings to be validated. Now police in the United Kingdom have begun to use the tactic to verify evidence in important court cases.
I. Industry's Silent Song
Recordings traditionally have been a highly unreliable form of evidence, given that they could easily be cleverly staged or tampered with.
That's where the hum comes in. Electrical sources such as light poles and power outlets emit a near imperceptible hum. While centered around the frequency of the alternating current (50 Hz in the UK), the hum dips and rises by a few thousandths of a hertz over time. The frequency drops when demand outpaces supply, and rises when supply outpaces demand.
Given a long enough window, this pattern of rising and falling frequencies is virtually unique, as Dr. Grigoras found.
[Image Source: UCSC Silicon Valley Extension]
But by using a technique called Electric Network Frequency (ENF) analysis, law enforcement can store the pattern of the hum
for a particular grid
in a database. The Metropolitan Police lab has been compiling such a database in recent years, as has JP French Associates -- another UK forensics lab.
JP French's Dr. Phillip Harrison to
, "We can extract [the hum from a recording] and compare it with the database - if it is a continuous recording, it will all match up nicely. If we've got some breaks in the recording, if it's been stopped and started, the profiles won't match or there will be a section missing. Or if it has come from two different recordings looking as if it is one, we'll have two different profiles within that one recording."
II. A New Time Stamp, but Could it be Gamed?
A trio of London gangsters -- Hume Bent, Carlos Moncrieffe and Christopher McKenzie -- recently saw their defense against London Metropolitan Police charges of gun dealing fall apart thanks to ENF. Dr. Alan Cooper, a Met Police ENF expert, validated police recordings of weapons deals using the grid buzz, scientifically damaging the defense's claim that the recordings were tampered with.
A trio of gun dealers were sentenced with the help of ENF verification of police evidence.
[Image Souce: PA]
The trio was founded guilty and sentenced to prison for a total of 33 years.
It seems appropriate the novel forensics method has been pioneered in the birthplace of fiction's Sherlock Holmes. But in years ahead, some questions about ENF remain unanswered. For example, while individuals would be unlikely to be able fake the ENF hum, it might be feasible, albeit extremely difficult, for a police force to filter out the hum in a recording and dub in a hum at the time they wish to make the recording appear from, given that they have access to the entire database of recordings.
It might be even possible for a citizen skilled in audio recording to carry out such a feat. Thus the technique may lay to rest questions of cruder tampering, but may still have flaws of its own. For that reason, in time it will probably be used as a piece of a richer evidence puzzle, also composed of other circumstantial clues like
cell phone tower records
This article is over a month old, voting and posting comments is disabled
he's making that face
12/14/2012 2:34:51 PM
The one on the right = black Zoolander.
RE: he's making that face
12/14/2012 4:25:08 PM
"There is a single light of science, and to brighten it anywhere is to brighten it everywhere." -- Isaac Asimov
Too Large to Manage? 1.3M Cell Phone Snooping Demands Filed in 2011
July 9, 2012, 2:23 PM
DOE Review: EVs, Grid Modernization to be Focus of 2013 Spending
September 30, 2011, 10:05 AM
London CCTV System Caught over 2,500 Criminals in 2010
December 28, 2010, 12:20 PM
Creationists are Mad About Google Doodle Depicting Evolution
November 24, 2015, 8:48 PM
DHS and TSA: Whoops, We Missed That 73 Airport Employees May be Terrorists
November 19, 2015, 2:16 PM
Star Wars Spinoff Film "Rogue One", Theme Park Attractions Announced
August 17, 2015, 12:20 PM
SpaceX Falcon 9's Seventh Supply Mission to ISS Ends w/ Fiery Stage 1 Explosion
June 28, 2015, 1:10 PM
Cool Science Video: Glowing Millipede Prowls the Nevada Desert
May 18, 2015, 12:00 PM
Newly Discovered Costa Rican Glass Frog is Kermit's Doppelgänger
April 22, 2015, 11:26 AM
Latest Blog Posts
Sceptre Airs 27", 120 Hz. 1080p Monitor/HDTV w/ 5 ms Response Time for $220
Dec 3, 2014, 10:32 PM
Costco Gives Employees Thanksgiving Off; Wal-Mart Leads "Black Thursday" Charge
Oct 29, 2014, 9:57 PM
"Bear Selfies" Fad Could Turn Deadly, Warn Nevada Wildlife Officials
Oct 28, 2014, 12:00 PM
The Surface Mini That Was Never Released Gets "Hands On" Treatment
Sep 26, 2014, 8:22 AM
ISIS Imposes Ban on Teaching Evolution in Iraq
Sep 17, 2014, 5:22 PM
More Blog Posts
Copyright 2016 DailyTech LLC. -
Terms, Conditions & Privacy Information