Geographic Grid Disambiguation
Definition
The process of determining which national or regional grid a recording's ENF trace came from, since the 50 Hz grids of continental Europe, the UK, and the Nordic region each drift independently and do not correlate with each other.
- Relevant method
- Electric Network Frequency (ENF) analysis
- Grids compared
- Continental Europe, UK, Nordic region
- Key fact
- Each grid drifts independently, uncorrelated with others
- Purpose
- Match a trace to the correct grid before comparison
Common questions
Why can't an ENF trace just be matched to any 50 Hz reference database?+
Separate synchronous grids, such as the Continental European, British, and Nordic grids, each have independent frequency fluctuations, so a trace must be matched against the correct grid's reference recordings or the comparison is meaningless.
How do examiners determine which grid a recording came from before matching?+
They may use case context such as the recording's claimed origin, distinctive drift patterns unique to a grid, or metadata, then verify the match against that specific grid's historical reference recordings.
What happens if a match is attempted against the wrong grid?+
The comparison produces a poor or spurious correlation because the two grids' fluctuations are independent, which can lead to an incorrect conclusion about authenticity or timing.
Related terms
- 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...
- Cross-Correlation
- A statistical measure of the similarity between two time series as a function of a time lag. In ENF matching, the extracted...
- 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...
- 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...