Problems of Forensic Sciences 2014 Vol. 98 (XCVIII) 106-117
THE POWERLINE HUM SIGNAL AND ENF DATABASE AS TOOLS USED IN THE FORENSIC ANALYSIS OF AUDIO RECORDINGS
Marcin MICHAŁEK
Institute of Forensic Research, Kraków, Poland
Streszczenie
The paper presents a study on the powerline hum signal, which may be registered on digital audio recordings. The described method of verification of the authenticity of questioned recordings is based on analysis of this signal, and is known as the Electric Network Frequency (ENF) criterion. Some aspects of the ENF criterion and a description of methods for acquisition and analysis of the hum signal are presented as well. Powerline hum is treated as unwanted noise by some people, but it can be a valuable source of information. Based on this signal, it is possible to check the integrity of a recording and establish when it was made. The paper presents the properties of the ENF database, which has been built up since 2009 at the Institute of Forensic Research in Kraków. Furthermore, the paper contains the results of tests conducted using various portable and stationary devices, i.e. voice recorders, mobile telephones, laptops, PC stations, a tablet and a video camera, and their ability to register the powerline hum signal. Software developed specially for this study was used for analysis of the hum signal.
Słowa kluczowe
Digital recording; Powerline hum; ENF database; Authenticity.