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
Score 1 for the good guys, 0 for the crimnals
12/16/2012 6:16:57 PM
Anything that helps prosecute criminals is fine by me. This could be used to prosecute numerous types of criminals in various ways and it's an excellent use of technology.
RE: Score 1 for the good guys, 0 for the crimnals
12/17/2012 2:23:04 PM
And what if the "criminal" hadn't actually committed a crime? What if that "criminal" was actually someone who just happened to be "in the wrong place at the wrong time"?
These guys have things like 17 years inside, that as far as we can tell has hints of being based upon "unreliable evidence".
Without knowing precisely what their phone line was like, what sort of bugging equipment was used, what sort of recording device was used, what sort of powering systems were used, how stable their local power supply is from voltage fluctuations, what sort of "editing" (if any) was carried out, how accurate the "50 Hz" database is, etc, it is impossible for us to know for absolute certainty whether these convictions are a true reflection of justice or not.
“So far we have not seen a single Android device that does not infringe on our patents." -- Microsoft General Counsel Brad Smith
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
Microsoft Co-founder Paul Allen Donates $100M to Fight Raging Ebola Epidemic
October 23, 2014, 6:05 PM
Cool Science Video of the Day: Carnivorous Leech Eats Giant Jungle Worm
October 16, 2014, 6:44 PM
Facebook CEO and Founder, Mark Zuckerberg, Donates $25M to Fight Ebola
October 14, 2014, 5:06 PM
Chagrined Over Leaks, CDC Confirms First U.S. Ebola Diagnosis in Dallas, Texas
September 30, 2014, 5:55 PM
Nail Polish May Soon be Able to Detect Date Rape Drugs
August 26, 2014, 7:57 AM
SpaceX Falcon 9-R Rocket Suffers Malfunction, Self-Destructs During Test Flight
August 23, 2014, 9:36 AM
Most Popular Articles
Amid Theater Boycott Netflix Defiantly Plans New Movies, Plus 3 TV Shows for 2015
October 24, 2014, 7:30 PM
AT&T Defeats Purpose of New Apple SIM, Locks iPad Air 2 SIMs to Its Network
October 24, 2014, 2:17 PM
CVS, Rite Aid Kill Unofficial Apple Pay Support, Burn Google Wallet Users in the Process
October 25, 2014, 5:26 PM
1 Million Credit Card Activated on Apple Pay Within 72 Hours, Walmart CEO Hopes Visa "Suffers"
October 28, 2014, 8:17 AM
Microsoft's Figures Show Desktop Users Flocking to Windows 10 Preview
October 27, 2014, 11:04 AM
Latest Blog Posts
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
Space Terrorism is a Looming Threat For the United States
Apr 23, 2014, 7:47 PM
More Blog Posts
Copyright 2014 DailyTech LLC. -
Terms, Conditions & Privacy Information