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Determination of time of recording with Electric Network Frequency (ENF). M.P. Huijbregtse BS, Zeno Geradts PhD AAFS Denver 2009. Outline. Introduction ENF Implications Research Conclusions. Conclusions. Introduction. Implications. Research. Introduction. Electricity network
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Determination of time of recording with Electric Network Frequency (ENF) M.P. Huijbregtse BS, Zeno Geradts PhD AAFS Denver 2009 Nederlands Forensisch Instituut Laan van Ypenburg 6, 2497 GB Den Haag
Outline • Introduction ENF • Implications • Research • Conclusions
Conclusions Introduction Implications Research Introduction Electricity network • Alternating current • Frequency • Europe 50 Hz • United States 60 Hz
Conclusions Introduction Implication Research Introduction ENF pattern
Conclusions Introduction Implication Research Introduction – prior research • C. Grigoras, Digital audio recording analysis – the electric network frequency criterion, International Journal of Speech Language and the Law, vol. 12, no. 1, pp. 63-76 (2005) • M. Kajstura, A Trawinska, J. Hebestreit, Application of the Electrical Network Frequency (ENF) Criterion – A case of a Digital Recording, Forensic Science International, vol. 155, pp. 165-171 (2005) • A.J. Cooper, The electric network frequence (ENF) as an aid to authenticating forensic digital audio recordings – an automated approach, Conference paper, AES 33rd International Conference, USA (2008)
Conclusions Introduction Implication Research Introduction
Conclusions Introduction Implication Research Introduction
Conclusions Introduction Implication Research Introduction • Conditions: • ENF pattern is the same in the whole network • ENF pattern is “unique” • ENF pattern can be filtered from a recorder
Conclusions Introduction Implication Research Implications – build a database
Conclusions Introduction Implication Research Implications – Build database
Conclusions Introduction Implication Research Implications Build a database
Conclusions Introduction Implication Research Software • Matlab • Java- applet for collecting, developed by us : www.sourceforge.net enf collector
Downsampling naar 300 Hz Bandpass filteren rond 50 Hz Spectrogram maken Piek frequenties bepalen Conclusions Introduction Implication Research Implications - filter
Conclusions Introduction Implication Research Implications – Filter signal Spectrogram:
Conclusions Introduction Implication Research Implications – filter signal
Conclusions Introduction Implication Research Implications – filter signal
Conclusions Introduction Implications Research Research - Questions • How unique is an ENF pattern ? • Is it possible to determine the time of recording ?
Conclusies Introductie Praktisch Onderzoek Implication Matching root mean square:
Conclusions Introduction Implications Research Implication - Uniqueness
Conclusions Introduction Implications Research Implication - Uniqueness
Conclusions Introduction Implications Research Implication best match • Recording of 3600 seconds:0.053 Hz < 0.080 Hz • Recording of 600 seconds:0.047 Hz > 0.040 Hz (!) • Recording of 60 seconds :0.015 Hz > 0.007 Hz (!)
Conclusions Introduction Implications Research Implication – Best match
Conclusions Introduction Implications Research Implication – Best match
Conclusions Introduction Implications Research Second method Correlationcoefficiënt:
Conclusions Introduction Implications Research Implication – best match
Conclusions Introduction Implications Research Conclusions • As in literature: • ENF pattern is the same in the whole network • ENF pattern can be extracted from network • Suggestions: • Matching of short recording (< 600 seconds) false hits are possible • Matching with the correlation coefficent better than root mean square error
Future research • Different recorders • (MP3) compression • Improvement of the current method