We all know of M.C Esher's Penrose stairs. Everyone at some point in life has traced the steps with their eyes in a way that could never happen in the physical world.
What happens when this visual illusion becomes an aural illusion? Meet the Shepard Tone .
No matter how long you listen, this tone will always be ascending. So what's the secret? Well, it's a number of different notes separated by octaves, creating an eerie chord. Each note rises in pitch as it its volume fades in, and then it will gradually fade out. However, it's impossible to hear these fade ins and fade outs as new notes replace the ones that disappear, making it hard for your ears to focus on one note and creating the illusion of the never ending aural staircase.
The Shepard tone has been used in a number of forms of media, including Super Mario 64, songs from The Beatles, and movies. After learning about the tone, you'll never look at the Batman trilogy from Christopher Nolan the same way again. The Shepard tone is constantly used in the score and also in the Batpod to make it sound like it's accelerating infinitely. Take a listen to this montage of Batpod sequences and listen for the strategically placed tone.
Any Shepard Tone references you know of or have discovered after learning about it? Let us know by leaving a comment!
Thumbnail photo by: Tatton Partington, Flickr