Content deleted Content added
Rescuing 0 sources and tagging 1 as dead. #IABot (v1.2.7.1) |
Deku-shrub (talk | contribs) No edit summary |
||
Line 4:
More recently, researchers demonstrated that indoor lights such as fluorescent lights and incandescent bulbs vary their light intensity in accordance with the voltage supplied, which in turn depends on the voltage supply frequency. As a result, the light intensity can carry the frequency fluctuation information to the visual sensor recordings in a similar way as the electromagnetic waves from the power transmission lines carry the ENF information to audio sensing mechanisms. Based on this result, researchers demonstrated that visual track from still video taken in indoor lighting environments also contain ENF traces that can be extracted by estimating the frequency at which ENF will appear in a video as low sampling frequency of video (25–30 Hz) cause significant aliasing.<ref>Garg Ravi, Varna Avinash L., Wu Min: {{cite web|url=http://dl.acm.org/citation.cfm?id=2072303|title="Seeing" ENF: natural time stamp for digital video via optical sensing and signal processing}}, Conference paper, in proceedings of the 19th international ACM Multimedia Conference, USA (2011)</ref> It was also demonstrated in the same research that the ENF signatures from the visual stream and the ENF signature from the audio stream in a given video should match. As a result, the matching between the two signals can be used to determine if the audio and visual track were recorded together or superimposed later.<ref>{{cite web|last=Garg |first=Ravi |title=Research Projects |url=http://www.ece.umd.edu/~ravig/Research.html |work=http://www.ece.umd.edu }}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
== Use by law enforcement ==
The distinctive electrical hums have been used to provide forensic verification of audio recordings, a process fully automated in the [[United Kingdom]].<ref>{{cite news|last1=Morelle|first1=Rebecca|title=The hum that helps to fight crime|url=http://www.bbc.co.uk/news/science-environment-20629671|accessdate=27 January 2017|date=12 December 2012}}</ref>
== References ==
{{reflist}}
| |||