Nothing grates on the ears and emotions quite like the sound of a human scream. Surprisingly, there is very little research on exactly why screams are alarming. They are loud and high pitched, but so are a lot of other noises. Now researchers have pinned down the unique qualities of a scary scream, reports Brady Dennis for The Washington Post.

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Researchers looked at YouTube videos, terrified yells from horror movies like Psycho and recordings from volunteers who let loose inside a sound booth. "We found that screams occupy a reserved chunk of the auditory spectrum, but we wanted to go through a whole bunch of sounds to verify that this area is unique to screams," David Poeppel, the lead researcher on the study, says in a press release. "In a series of experiments, we saw [that] this observation remained true when we compared screaming to singing and speaking, even across different languages."

Singing, speaking and other speech sticks to the range between four and five hertz, but screaming ranges from 30 to 150 hertz. The rapid changes along that range give human screams an acoustical quality called "roughness." The researchers published their work in the journal Current Biology. Dennis reports:

Researchers tested musical instruments, traffic noises and other sounds to see if anything else displayed similar roughness to human screams. Singers such as Tom Waits and Steven Tyler at times come close. The only other sounds that showed similar modulation were car alarms, house alarms and alarm clocks, whose creators intuitively have figured how to trigger human fear.

When the team asked another group of volunteers to rank how scary they found different scream recordings, they found that the "roughest" sounds, the ones that change the most in frequency, corresponded with the scariest. But not all the emotions spiked by rough nosies are negative, reports Nsikan Akpan for PBS Newshour. Dissonance in rock music also shows rough qualities, explains research team member Luc Arnal, a neuroscientist at the University of Geneva. "We might add these unpleasant sounds because they move us,” he tells Akpan.