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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

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
Outline Frequency (ENF)

  • Introduction ENF

  • Implications

  • Research

  • Conclusions


Introduction

Conclusions Frequency (ENF)

Introduction

Implications

Research

Introduction

Electricity network

  • Alternating current

  • Frequency

    • Europe 50 Hz

    • United States 60 Hz


Introduction1

Conclusions Frequency (ENF)

Introduction

Implication

Research

Introduction

ENF pattern


Introduction prior research

Conclusions Frequency (ENF)

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)


Introduction2

Conclusions Frequency (ENF)

Introduction

Implication

Research

Introduction


Introduction3

Conclusions Frequency (ENF)

Introduction

Implication

Research

Introduction


Introduction4

Conclusions Frequency (ENF)

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


Implications build a database

Conclusions Frequency (ENF)

Introduction

Implication

Research

Implications – build a database


Implications build database

Conclusions Frequency (ENF)

Introduction

Implication

Research

Implications – Build database


Implications build a database1

Conclusions Frequency (ENF)

Introduction

Implication

Research

Implications Build a database


Software

Conclusions Frequency (ENF)

Introduction

Implication

Research

Software

  • Matlab

  • Java- applet for collecting, developed by us : www.sourceforge.net enf collector


Software1
Software Frequency (ENF)


Implications filter

Downsampling naar 300 Hz Frequency (ENF)

Bandpass filteren rond 50 Hz

Spectrogram maken

Piek frequenties bepalen

Conclusions

Introduction

Implication

Research

Implications - filter


Implications filter signal

Conclusions Frequency (ENF)

Introduction

Implication

Research

Implications – Filter signal

Spectrogram:


Implications filter signal1

Conclusions Frequency (ENF)

Introduction

Implication

Research

Implications – filter signal


Implications filter signal2

Conclusions Frequency (ENF)

Introduction

Implication

Research

Implications – filter signal


Research questions

Conclusions Frequency (ENF)

Introduction

Implications

Research

Research - Questions

  • How unique is an ENF pattern ?

  • Is it possible to determine the time of recording ?


Implication

Conclusies Frequency (ENF)

Introductie

Praktisch

Onderzoek

Implication

Matching root mean square:


Implication uniqueness

Conclusions Frequency (ENF)

Introduction

Implications

Research

Implication - Uniqueness


Implication uniqueness1

Conclusions Frequency (ENF)

Introduction

Implications

Research

Implication - Uniqueness


Implication best match

Conclusions Frequency (ENF)

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 (!)


Implication best match1

Conclusions Frequency (ENF)

Introduction

Implications

Research

Implication – Best match


Implication best match2

Conclusions Frequency (ENF)

Introduction

Implications

Research

Implication – Best match


Second method

Conclusions Frequency (ENF)

Introduction

Implications

Research

Second method

Correlationcoefficiënt:


Implication best match3

Conclusions Frequency (ENF)

Introduction

Implications

Research

Implication – best match


Conclusions

Conclusions Frequency (ENF)

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
Future research Frequency (ENF)

  • Different recorders

  • (MP3) compression

  • Improvement of the current method


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