You know that feeling you get in your gut when you think something bad is about to happen? Or a feeling of paranoia when watching a horror film? These feelings are created through very careful manipulation of a few elements such as camera shots, use of music, silence etc. As it turns out, in many cases, the scariest sounds in horror films are in fact the ones we cannot hear. Sound designers are beginning to reveal that they are using what is called "infrasound" to make their movies seem more frightening.
What is Infrasound?
Infrasound refers to sound waves that occupy a frequency that cannot be heard by the human ear. While our ears may not perceive these sound waves, our bodies do. Thus when exposed to an infrasonic frequency, it is known to create a rumbling feeling in our stomach that cause feelings of fear and dread. These sound waves must occupy a frequency below 20 Hz to be considered infrasonic/inaudible to human ears. If you are listening to something with an infrasonic frequency, most people feel a sense of relief-as if a weight has been lifted off their chest-when the track is turned off.
Infrasound & Ghosts
There is a story of a researcher named Vic Tandy whom worked in a library that was supposedly haunted, and he thought he saw something move at the corner of his eye. In search of a scientific explanation, he discovered that a fan in the library was producing an infrasonic frequency of 18.98 Hz (1.02 Hz below what humans can hear). Not only does this frequency cause feelings of fear and discomfort, this frequency is also known to cause optical illusions. Thus in scary movies, this is why we may feel paranoid during certain movie scenes. If you wish, grab some headphones, and click below to listen to "The Ghost Frequency" (18.98 Hz) and experience the effects of infrasound.
(Please proceed at your own caution. This video is known to cause discomfort in many listeners. If you begin to feel sick, I advise you to turn it off)
Infrasound in Nature
While humans are unable to hear infrasound, other species can both hear these frequencies and use them to communicate. For example, Elephants actually use infrasound to send signals that can travel through solid ground that are felt by other elephants through their feet. The whale, hippopotamus, giraffe, rhinoceros and okapi all use infrasonic frequencies to communicate from great distances. Other sources of infrasound in nature include volcanos, earthquakes, ocean storms, etc.
Movies
Sound designers for movies such as Paranormal Activity and The Conjuring II have admitted to using infrasound to scare audiences. Seeing as movie theatres have tremendous speaker systems, infrasonic frequencies are capable of reaching every audience member just as easily as the frequencies they can hear. The fact that the illusion of silence and high feelings of fear can sweep an entire audience through infrasound is both manipulative and haunting.
Next time you are watching a scary movie, consider the possibility that you may not be hearing everything that is trying to scare you. If you have an unsettling feeling in your stomach, you may in fact be under the spell of infrasound.