Cross-Correlation
Definition
A statistical measure of the similarity between two time series as a function of a time lag. In ENF matching, the extracted frequency trace from the recording is cross-correlated with sections of the reference database to find the position of highest similarity, identifying the probable recording window.
- Measures
- Similarity between two time series as a function of time lag
- Forensic use
- ENF trace matched against reference frequency database
- Output
- Position of highest similarity between recording and reference
- Field
- Signal processing, audio authentication
Common questions
Why does a high cross-correlation peak indicate a probable recording time in ENF analysis?+
Because the mains electricity frequency fluctuates in a distinctive, non-repeating pattern over time, so a strong match between the recording's extracted trace and a specific segment of the reference database suggests the recording captured the grid at that particular moment rather than at any other time.
What can produce a false or ambiguous cross-correlation peak in ENF matching?+
Short recordings, noisy audio with a weak ENF signal, or a reference database with gaps can all produce a low-confidence or misleading peak, which is why analysts report a correlation strength alongside the matched time window rather than treating any peak as certain.
Is cross-correlation used only for ENF analysis in forensic audio work?+
No, it is a general signal-processing technique also applied to compare and align other paired signals, such as matching an audio recording against a suspected source device's characteristic noise profile or synchronising multiple recordings of the same event.
Related terms
- Electric Network Frequency (ENF)
- The instantaneous frequency of the alternating-current mains supply, nominally 50 Hz in most of the world and 60 Hz in North America....
- ENF Reference Database
- A continuously maintained archive of grid frequency measurements recorded at high temporal resolution, used as the ground truth against which a recording's...
- Camera Flicker / Optical ENF
- The periodic brightness variation captured in video recorded under mains-powered fluorescent or LED lighting. The lighting modulates at 100 Hz or 120...
- ENF Discontinuity
- A break in the continuity of the extracted ENF trace that is inconsistent with the reference database. Can indicate a deletion (missing...
- ENF Splice Detection
- Using breaks or discontinuities in the ENF time series to identify edits, cuts, or inserted segments in a recording. A genuine unedited...
- Geographic Grid Disambiguation
- The process of determining which national or regional grid a recording's ENF trace came from, since the 50 Hz grids of continental...
- Short-Time Fourier Transform (STFT)
- A signal processing technique that applies a Fourier transform to successive short windows of a signal, producing a time-frequency representation. Used in...
- Transmission System Operator (TSO)
- The entity responsible for operating a high-voltage electricity transmission network in a given country or region. TSOs log grid frequency in real...
Explained in these topics
- Audio Authentication and the Electric Network Frequency MethodA mathematical sliding-window comparison that measures the similarity between two time series at every possible time offset. In ENF analysis it finds the posit...
- Electric Network Frequency Analysis for Audio Dating