ENF (Electric Network Frequency) Analysis
Definition
A method that tracks the recorded mains-frequency component (nominally 50 Hz or 60 Hz) through an audio file and compares its fluctuation pattern against a time-stamped reference database. Breaks in the ENF pattern, or a pattern spanning multiple non-contiguous time windows, indicate that segments from different recording sessions have been joined.
- Signal tracked
- Mains-frequency hum embedded in the audio
- Nominal frequency
- 50 Hz or 60 Hz depending on region
- Comparison basis
- Time-stamped ENF reference database
- Tamper indicator
- Breaks or non-contiguous matches in the pattern
Common questions
What does a match to a single continuous database window prove?+
It supports that the recording is continuous and was made when and where the reference database says, but it does not by itself authenticate the content or rule out edits made without disturbing the ENF trace, such as an edit at a point where the frequency happened not to change.
Why does ENF analysis need region-specific reference databases?+
Grid frequency drift patterns differ between separately synchronised grids, so a recording made on the European 50 Hz grid cannot be matched against a North American 60 Hz database, and even within one nominal frequency, different interconnected grids drift independently.
Related terms
- Background Noise Profiling
- Statistical characterisation of the ambient noise floor in quiet segments of a recording, including its average level, spectral shape, and stationarity. Changes...
- Discontinuity
- Any point in an audio recording where a physical property of the signal changes abruptly in a way inconsistent with natural acoustic...
- Phase Discontinuity
- An abrupt change in the phase of a periodic component of the audio signal. In a continuous recording, the phase of background...
- Room-Tone Tail
- The natural reverberation that follows a sound event in an enclosed space. Each room has a characteristic decay time and spectral shape....
- Spectrogram
- A time-frequency plot in which the horizontal axis is time, the vertical axis is frequency, and colour or brightness encodes signal energy....