The Shepard Tone
There are many audio illusions, each with different effects, that can help us explore exactly how our brains work. Auditory illusions are interesting in that they trick the brain into believing it is experiencing an auditory phenomenon that is not actually present. Take for example the belief that an audio piece is continually rising, when in fact the audio is looping. This unique auditory illusion is known as the Shepard tone, and believe it or not you’ve probably heard at least one before.
The Shepard tone is a unique phenomenon with audio that makes it sound as if the pitch is infantilely raising or lowering. The Shepard tone is an auditory illusion loop that is comprised of multiple sine waves that are separated by an octave. These same waves are layered on top of one another. In the event there are three tones there is a high, middle, and low tone. As the tone plays the highest tone slowly fades until it is completely silent, at the same time the lower tone gradually increasing in volume. When this is looped our brain is tricked into believing we are hearing an infinitely rising pitch because we are, in fact tearing two tones rising in pitch. Naturally, this works in reverse if you are hearing a Shepard tone that sounds like it is continuously lowering.
Shepherd tones have been used in many settings including films and video games. They have an interesting effect. In many cases, a Shepard tone creates tension and is ideal for settings needing that added element. A Shepard tone can also have some intriguing impacts on people if they listen to it for a prolonged period of time. Some have claimed that they feel anxious, sick or even dizzy. These physical effects likely manifest as our brain struggles to comprehend the auditory illusion.