Every bolt of lightning is a radio transmitter. When lightning strikes, a huge pulse of electric current flows for a fraction of a second, and that pulse throws off a burst of radio waves. Most of that energy lands in the very low frequency (VLF) range, roughly 3 to 30 kHz. Those frequencies happen to sit right where human hearing does, so if you catch them with an antenna and feed them into a speaker, you can actually hear lightning.
That's what every Sferic Supply recording is: real thunderstorms, heard as radio.
Sferics: the sound of a lightning strike
The radio burst from a single lightning strike is called a sferic, short for "atmospheric." Through a speaker it sounds like a sharp pop, click or crackle. During an active storm there can be dozens a second, and together they sound like bacon frying, rain on a tin roof, or a campfire made of electricity.
Worldwide, lightning strikes roughly forty to fifty times every second, so somewhere on Earth there is always a storm, and a sensitive VLF receiver almost always hears a background crackle of distant lightning.
How a strike hundreds of miles away reaches the antenna
VLF radio waves don't just fade out over the horizon. They get trapped between two conducting layers: the ground below and the ionosphere above, a layer of electrically charged gas that starts about 40 to 50 miles up. The space between them acts like a giant waveguide wrapped around the planet. A sferic can bounce along inside it for hundreds or even thousands of miles, which is why many of the crackles in our recordings come from storms far beyond the horizon.
Tweeks and whistlers: the stranger sounds
Natural radio has a few rarer voices, too:
- Tweeks are sferics that traveled a long way through the waveguide at night. The trip stretches them out so they end in a short, musical "ping" or chirp.
- Whistlers are the most famous. Some lightning energy escapes up into space and follows Earth's magnetic field lines out to the far side of the planet and back. Along the way, higher frequencies outrun lower ones, so the sharp click is smeared into a falling tone that sounds like a slide whistle, lasting up to a few seconds.
On a quiet night far from power lines, a VLF receiver can also pick up the dawn chorus, a rising, birdsong-like sound made by charged particles in Earth's magnetosphere.
How our recordings are made
The Sferic Supply listening station is completely homemade. The antenna started life as an old hay feeder sitting unused in a field on the farm. Wound with about 275 feet of copper magnet wire, it became a large loop antenna standing in a clearing in the woods in rural Tennessee. Next to it, a weatherproof cabinet holds a small computer and a high-resolution sound card that records the antenna's signal 192,000 times a second, all through the summer storm season.
Back at the desk, the recordings get the same care as a studio session:
- Power-line hum is filtered out, since a nearby power grid buzzes loudly at 60 Hz and its harmonics.
- Levels are matched so clips sit comfortably side by side.
- The busiest, most dramatic stretches of each storm are found and cut into clips.
Nothing is synthesized, layered or added. Every crackle you hear is a real lightning strike.
Seeing the sound: spectrograms
A spectrogram is a picture of sound. Time runs left to right, pitch runs bottom to top, and brightness shows how loud each frequency is. A lightning strike hits every frequency at once, so each sferic shows up as a thin vertical line. A busy storm turns into a forest of glowing lines, which is exactly what you see in our storm prints.
Hear it and hang it
Every product in the shop comes from these recordings:
- Storm Sounds: royalty-free sound packs and long ambient recordings for sound design, film, games, sleep and focus.
- Prints: the storms themselves, drawn as spectrogram art, framed or unframed, plus a three-panel triptych.
- Radio & Weather Gear: lightning detectors, weather stations, and books for anyone who wants to build their own antenna and start listening.
Recorded by Leslie Fletcher, amateur radio operator KR4JDK.