How Horror Movies Like undertone Use Sonic Science To Scare The Hell Out Of Us
Hoarse whispering and harsh static are practically guaranteed to scare audiences. But what is driving these reactions?
There’s an art to scaring people with sound. Directors like James Wan and Hokum’s Damian McCarthy have made careers out of skillfully manipulating the sound mixes in their films, building tension with silence and then breaking it with loud, assaultive sound. Earlier this year, another horror movie — A24’s undertone — took this phenomenon to the next level, taking a modest indie production (the film was made for just $500,000) and juicing it up with a Dolby Atmos sound mix designed to maximize the movie’s scares.
Although it does make evocative use of shadows and empty space, undertone’s storytelling is primarily audio-based. The story revolves around a podcaster named Evy (Nina Kiri) who’s staying in her childhood home caring for her dying mother. As so many are, the podcast is all about strange phenomena and bizarre true stories. As the show’s “resident skeptic,” Evy is usually immune to creepy things like the series of 10 audio recordings her co-host Justin (Adam DiMarco, heard but never seen) introduces in their latest episode. But something is different about these files, which we listen to alongside Evie as the terror escalates alongside the bizarre and jarring nature of the sounds themselves.
The technique works: As Inverse’s Hoai-Tran Bui writes in her review, the scariest moment in the movie features no visuals at all, simply “screams and inhuman noises” over a black background. “It’s a testament to the film’s pristine audio production (best seen in Dolby Atmos, or better yet, through your own headphones) that such a scene can be so terrifying and chilling with nothing happening on screen,” she writes.
The word “inhuman” is key here: As Dr. Dan Blumstein, a professor in the Department of Ecology and Evolutionary Biology at UCLA, tells Inverse, “we are the product of evolution that's worked for billions of years of life on Earth. We are the successful descendants of those that got their risk assessment right.” So when we hear an unfamiliar noise, particularly if it also sounds angry (discordant) and/or big (loud), “we innately respond” with what can rather simplistically reduced to a “flight-or-flight response.” Parked in a movie-theater chair, these instinctual responses have nowhere to go: Our palms sweat, and our pulse quickens, prompting the release of cortisol and adrenaline and leaving our bodies in a state of heightened arousal. But we don’t get up to leave — not usually, anyway.
Blumstein’s work revolves specifically around the phenomenon of nonlinear frequencies — static is a common example — which he defines as “predictably unpredictable” patterns of noise caused by overloading a mammal’s vocal cords. “You vibrate your vocal folds in your throat, and you're changing the shape of your oral tract. That changes the sound. But when you blow too much air over your vocal folds and they vibrate too much ... that sort of lack of control seems to be associated with fearful sounds,” Blumstein says.
Nonlinearities are “particularly evocative” because they mimic “systems that are stressed, and that communicate stress and arousal,” Blumstein says. “The frequencies break. You get noisy, staticky things in the vocalizations of animals that are screaming, [as well as in] human screams. Nonlinearities are the secret sauce of the acoustics of fear, which people can replicate in music and [sound effects].” If you’ve ever seen a horror movie where a character turns on a TV or a radio to the sound of loud static, that director — whether they knew it or not — was priming an evolutionary response that goes back millennia. Think also of the discordant strings in Bernard Herrmann’s famous “Psycho Theme,” or the random bursts of squealing violin in the score for Friday the 13th.
In the case of undertone, technology also played a role: Director Ian Tuason says that the creepy, garbled recordings Evy investigates in the film came straight from his iPhone, and the relatively lo-fi files are scarier because they’re full of interference. The sound of “the mic rubbing against [the actor’s] hand, or the fabric of [their] clothes” adds a “rustling, scraping sound,” Tuason says, adding that “just the room tone of an iPhone has a texture to it” that’s different from — and, therefore, more distressing than — the ambient background sound that you get from a professional-quality mic.
Directional sound was also very important to the improved sound mix created for undertone’s theatrical release: “There were a lot of things that I wasn't able to do [in surround sound],” Tuason says. “We played around more with direction [in the final mix]. I wanted to put the banging directly above you. I can only do that with Dolby Atmos.” Another big change, according to Tuason, was turning up a “low rumbling” on the soundtrack and adding a beat to it, so that “it was mimicking footsteps from an entity.” (According to Blumstein, the science of this trick is straightforward: “If something is low frequency, it must be big. And big things scare us, because dominance is all about size.”)
There’s also a lot of creepy whispering, which Blumstein hasn’t studied specifically but theorizes may be upsetting because it’s a violation of the unique human phenomenon of personal space. (“A lot of the whispers that animals are doing are nice things, rather than scary ones,” he says.) Blumstein’s initial research into the link between evolutionary biology and scary sounds revolved around marmots, a type of large ground squirrel common across much of the world.
Then he teamed up with composer Peter Kaye and communications professor Greg Bryant, and the trio devised an experiment where human subjects were asked to listen to two pieces of music: An “emotionally neutral” score, and one featuring the nonlinear elements Blumstein had already identified as distressing to marmots. In humans, the results were similar, as the nonlinear sounds consistently stressed listeners out more than the linear ones.
By comparison, Tuason’s method is much more intuitive: “I knew what sounds would scare me,” he says. “There's not much else I need to do except let people hear them.”
