Tracking of electrical network frequency for the purpose of forensic audio authentication

Establishing the authenticity of audio evidence is a task of paramount importance in the field of audio forensics. A relatively new approach to establishing the authenticity of digital, as well as analog, audio recordings is the method of Electrical Network Frequency (ENF) analysis. The method is based on tracking the variations of the ENF in the mains hum present in the questioned recording, and comparing the track to a database of referent ENF recordings made directly from the power grid in the time period in question. The paper proposes one such system, designed to log the ENF track in high quality directly from the power lines. The signal conditioning modules provide several functions, such as: attenuation, galvanic isolation, filtering, A/D conversion etc. In this paper, directions for proper dimensioning of the signal conditioning modules are presented. Additionally, a prototype realization of a signal conditioning circuit and its characteristics are given. The power line signal recording for the purpose of audio authentication was realized by using a LabVIEW based virtual instrument.