What Electrical Hum Can Reveal About a Recording
Many recordings contain a faint tone from the electrical power system. In places using alternating current, the grid cycles at a steady frequency, and nearby equipment can leave that rhythm—and sometimes its harmonics, higher tones related to it—in a microphone’s signal. The result can act like an incidental time marker embedded in the audio.
Forensic analysts can compare that pattern with records of how the grid frequency changed over time. If a recording’s hum follows one period’s fluctuations, but a section appears to follow a different period, that may indicate the audio was joined, altered, or assembled from separate recordings. The technique is often called electric network frequency analysis.
Why a Mismatch Is Only a Clue
The comparison depends on the hum being present and measurable. A microphone may capture little of it; noise reduction, compression, or other processing may weaken or distort it. A recording made on battery-powered equipment may have no useful grid signal at all. Even when a mismatch appears, ordinary recording conditions or technical limitations can complicate the interpretation.
That is why analysts treat the result as one piece of evidence, not a verdict. They may examine the file’s structure and other acoustic signs as well, then explain what the data supports and what it cannot establish. Software can help detect patterns across a recording, but no single test can reliably label every heavily manipulated file as genuine or fake. The practical value is narrower and more useful: a subtle electrical trace can point investigators toward a segment that deserves closer scrutiny.
