A strange name, with a simple premise. A ‘normal’ microphone captures changes in pressure in the air. What if we used a device that captures changes in electromagnetic fields? This may sound complicated, but its quite simple. In fact, this very principle is used by guitar pickups; Coil pickups. Utilizing a coil of wire, we can convert electromagnetic fluctuations into voltage fluctuations, and therefore audio signals.
Coil pickups act a little strange at first, for someone used to using microphones to record sounds. A guitar pickup captures not the air pressure differences of the strings vibrating, but the electromagnetic fluctuations of the string oscillating past the pickup. It just so happens that both of those fluctuations, converted to voltage, sound almost exactly the same. A few objects provide this result, such as motors. The differences come from non-electrical objects, and non-mechanical electrical objects. Humans, for instance, make no sound whatsoever (out electromagnetic fluctuations are far to weak to be picked up). Likewise, digital components makes no sound pressure waves that can be measured with a microphone, but enormous amounts of electromagnetic fluctuations, as seen below:
As the controller operates on a fixed clock speed, steady(ish) tones are produced. However, whenever we interact with the panel, addition information is processed, and a change in timbre is heard.
This entire premise is explored in Christina Kubisch’s Electrical Walks (https://christinakubisch.de/electrical-walks). The participants wear modified headphones with coil pickups and amplifiers built in, and walk a curated route around a city, hearing only the sounds produced by electromagnetic fields. Each city sounds different.
The overall result of this is a symphony made up of invisible forces that pass through and around us daily, entirely unnoticed. And by using such a simple piece of technology, we can now perceive an entirely new world.