Hello You.

Last week we buried the music magazines. Three weeks ago, THE STAIRCASE gave you dread you could hear. This week it’s the kind you can’t.

So let's talk about 19Hz.

The lab

Vic Tandy was an engineer. Practical. Not a ghost guy. The lab he worked in already had a reputation. People said it felt wrong in there. One of the cleaners had left shaken, sure she’d seen something.

One night he was working late, alone, when it got him too. He was sweating but cold. A heavy, gloomy feeling he couldn’t explain. Then something grey appeared at the edge of his vision. It took him a while to work up the nerve to turn and face it. When he did, it faded away.

He went home convinced he was cracking up. He came back the next day with a fencing foil to fix, because of course the man fenced. He clamped it in a vise. And the blade started shaking on its own.

Not a poltergeist. A fan. The lab had just installed a new extractor fan, and it was putting out a standing wave at about 19Hz, a sound wave bouncing around the room and stacking up on itself. They switched the fan off and the wave went away.

He wrote it up with psychologist Tony Lawrence in 1998. They called it “The Ghost in the Machine.” We're obviously a big fan of this.

For fun, or just to say it had no impact on you, here is 19Hz to listen to. We listened while we were researching this. It really needs to be on a sub of some type for it to work but use what you have and see for yourself.

Sound you can’t hear

19Hz is infrasound. Human hearing bottoms out around 20Hz (not for everyone), so anything below that slips under the floor. Your ears don’t pick it up. But we can still feel it, which is cool and uncomfortable at the same time.

Tandy took a sound meter into a 14th-century cellar in Coventry. It sat under the city’s tourist information centre, and the staff were sure it was haunted. The meter found 19Hz there too.

One fan and one cellar is a story, not science. So in 2003, a team in London did something a bit more unhinged. They held a concert.

750 people in the Purcell Room. Four pieces of music. Under two of them, a 17Hz tone pumped out of a 7-meter pipe. Nobody knew which two. For the second show they swapped them around, so it couldn’t be the music doing it.

When the tone was on, strange experiences went up 22%. Unease. Sorrow. Chills down the spine. A room full of people uneasy about something, but to their mind it was nothing they heard.

The new bit

This April, researchers at MacEwan University in Canada ran it again. 36 students sat alone listening to music, some calming, some unsettling. For half of them, hidden subwoofers played 18Hz underneath.

Nobody could say "oh I heard this", 'cause you can't, but your brain sure does know it is there. The infrasound group got more irritable, more uncomfortable, and rated the music as sadder. Even the calming music. Their cortisol, the stress hormone, went up.

What they didn’t find was fear. Just a sour, prickly mood with no clear cause. Which is somehow worse. A haunted house doesn’t need to scare you into leaving, not really, it just needs to make you feel like you shouldn’t be there.

Dread is not terror

Terror is a scream. And a scream has its own sound.

In 2015, neuroscientist Luc Arnal found that screams aren’t scary because they’re loud or high. It’s roughness: how fast the volume flickers. Normal speech wobbles 4 or 5 times a second. A scream flickers 30 to 150 times a second. The rougher the scream, the scarier people rated it, and the harder it lit up the amygdala, the brain’s fear alarm. Car alarms are built on the same flicker. Kinda weird, but it makes sense: hear alarm, panic.

Terror arrives in an instant. It’s a scream, a crash, a sound with a source. Your body spikes, and then it’s over.

Dread never arrives, it just hangs there, holding on. In THE STAIRCASE it came from the music promising a payoff it never delivered. Here it’s even simpler. Your body is told something is wrong, and there’s nothing to point at. No scream. No monster. No sound at all.

Filmmakers knew

PARANORMAL ACTIVITY (2007) barely has a soundtrack. What it has is a low rumble that rolls in seconds before something happens.

When Denis Villeneuve asked Jóhann Jóhannsson to score SICARIO, the brief was music you could feel as much as hear. Jóhannsson built it from the bottom of the orchestra: eight basses, ten cellos, contrabassoon, contrabass clarinets, tubas. He described the result as a beast lurching at you in slow motion. The track is called THE BEAST. It’s first on the playlist, which was trickier than normal to make because what we're trying to get you to listen to, can't be heard.

Your turn

You’ve already had a go at 19Hz on its own up top. Now stack it.

Do what we did. Open the sub-audible track and Bangalter’s track (yeah, the Daft Punk guy) from the IRRÉVERSIBLE movie in two tabs and press play on both. Bangalter’s unsettles you all by itself with those rolling wubs. The sub-audible one just feels heavy. Headphones work, a proper subwoofer works better. Keep the volume sensible though, and notice when you start to feel something.

We spent a full day playing with these sounds, fun, yes, and at times uncomfortable. We've selected songs that play with textures, layers, and deeper tones. We'd say enjoy but that's not really the point.

Dread first, terror second. Hear the difference.

See you next Thursday.

The reading, if you want to go deeper: