The hidden background noise that can catch criminals

Summary by Krater

Tom Scott explores whether audio recordings can be timestamped using mains hum (electrical network frequency) data from the National Grid, testing forensic experts with real video footage.

From the video

Answers: Can audio recordings be timestamped using electrical mains hum?

• Electrical mains hum
• ENF (electrical network frequency) trace analysis
• Forensic audio analysis
• National Grid historical frequency data
• Signal processing algorithms

What it concludes

• Mains hum and its harmonics can be used in forensic audio analysis to timestamp recordings against historical National Grid frequency data.
• Longer audio recordings yield more reliable timestamping results, with one minute being an absolute minimum.
• Edits in an audio recording can be detected by sudden jumps in the ENF frequency trace or an abrupt stop in the trace.