Sound Illusions

Scale Illusion
This illusion was discovered by Diana Deutsch, and is an example of our brains “grouping” similar notes together. Two major scales are played: one ascending, one descending. However, the notes alternate from ear to ear.


Phantom Melodies
Some pieces of music consist of high-speed arpeggios or other repeating patterns, which change only subtly. If they’re played fast enough, the brain picks up on the occasional notes that change, and links them together to form a melody. The melody disappears if the piece is played slowly.


Shepherds Ascending Tones
This is a recording of Shepard’s paradox synthesized by Jean-Claude Risset. Pairs of chords sound as if they are advancing up the scale, but in fact the starting pair of chords is the same as the finishing pair. If you loop this sample seamlessly then it should be impossible to tell where the sample begins and ends.


Falling Bells
This is a recording of a paradox where bells sound as if they are falling through space. As they fall their pitch seems to be getting lower, but in fact the pitch gets higher. If you loop this sample you will clearly see the pitch jump back down when the sample repeats. This reveals that the start pitch is obviously much lower than the finishing pitch.


Quickening Beat
This recording is subtle. A drum beat sounds as if it is quickening in tempo, but the starting tempo is the same as this finishing tempo. Listen carefully.


Virtual Barbershop
This is a demonstration of the stereo effect. Listening to it, you feel as though you are in a barber’s chair, with the barber moving around you, clipping away at your hair. As the barber “moves” to your right, the volume increases slightly in the right channel and decreases in the left. Similarly, increases in the volume of sound from the clippers give the impression that he is bringing them closer and closer to each ear. The illusion demonstrates our ability to locate sounds in space; by comparing the inputs to the two ears, we can work out where a sound is coming from.

Matchbox Rattle
This, like the barbershop above, is another stereo illusion. In this illusion a man shakes a matchbox all around your body and lights matches occasionally.


Tritone Paradox
This illusion was also discovered by Diana Deutsch. In this recording, some people hear the two notes going from low to high, while others hear them going from high to low. The is a good one to listen to in a group so you can compare notes afterwards. The notes being played are called the tritone – it falls exactly in the middle of a standard musical scale. This note was once considered to be evil and was not used in music until modern times.

Phantom Words
This illusion was first demonstrated by Diana Deutsch at the University of California, San Diego. The recording features overlapping sequences of repeating words or phrases, located in different regions of stereo space. As you listen to it, you’ll start to pick out specific phrases. However, none of the phrases are really there. Your brain is constructing them, in a bid to make sense of a meaningless noise. Indeed, you may find that the phrases you hear are related to what’s on your mind – for example, people who are dieting often hear phrases associated with food. This can be a very eerie experience.


Sound for under 20s Only
This is a sound that can only be heard by people under 20 (some over 20 can hear it but not many) – it is a sine wave at 18,000 Hz (by comparison, a dog whistle sounds at 16,000 – 22,000 HZ – meaning your dog can hear this “under 20s” sound as well). This sound is used by some teenagers as a ring tone on their mobile phone so that only they (and others of their age group) can tell when the phone is ringing. It is also occasionally used in England to play very loud in areas that authorities don’t want teens to congregate in,