“Many of our electrical things, all around us, are constantly buzzing at 60 hertz, or a harmonic like 120 hertz. And what we’re hearing, or not hearing, is the electrical grid. The companies that manage our power, in my case, Con Edison in New York, are required by law to maintain that 60 hertz output” — thus Micah Loewinger explains the foundation of a fascinating audio forensics tool called ENF, which stands for electrical network frequency analysis.
Essentially, there’s a record of slight variations in the electrical grid, and by mapping a recording’s underlying buzz against the historical record, sleuths can identify the date and time — “almost to the exact second,” reports Loewinger — that something was taped. It’s an intriguing story about evidence hiding in plain sight, and about the way sounds that we take for granted contain meaning.
Listen to the full episode (transcript also available), which aired recently as part of the WNYC show On the Media (and which, as a bonus, opens with another sound-related story: an update on “The Unending Mystery of Havana Syndrome”). (Thanks, Rich Pettus!)