We have put together an amazing list of sound illusions (auditory illusions). In these illusions, your mind is tricked into thinking it is hearing something when, in fact, it is not. To get the most out of this list you should have a set of stereo headphones or a stereo sound system with speakers set at a distance, but headphones are preferred. Laptop speakers are not suitable for most of these illusions. So without any further delay, here we look at the top 10 audio illusions:
1. Shepard’s 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. It seems like the tone is ascending even if you loop the sample on your audio player.
2. 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. The illusion can be felt if the sample is looped in an audio player.
3. Quickening Beat
This recording is subtle. A drumbeat sounds as if it is quickening in tempo, but the starting tempo is the same as the finishing tempo. The increase in tempo can be felt if the sample is looped in an audio player.
4. Shaking Matchbox
In this illusion, a shaking matchbox is moved around your entire body. It’s so realistic that you really feel an invisible/virtual matchbox moving around your body.
5. Phantom Melodies
Some pieces of music consist of high-speed arpeggios or other repeating patterns, which change only subtly. If they’re playing 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.
Compare these recordings of Christian Sinding’s Frühlingsrauschen (“Rustle of Spring”). At the higher speed, the changing notes linger in your perception long enough to be linked into a melody, but at the lower speeds, they’re too widely separated.
6. Virtual Haircut
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.
7. Scale Change 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, and one descending. However, the notes alternate from ear to ear – for instance, the right ear hears the first note of one scale, and then the second note of the other.
There are several ways in which people perceive these sounds, but the most common is to group the high and low notes together. Rather than hearing the two scales, people hear a descending and re-ascending melody in one ear, and an ascending and descending melody in the other. In other words, the brain reassigns some of the notes to a different ear in order to make a coherent melody. Right-handed people tend to hear the high melody in the right ear, and the low one in the left, while left-handers show a more diverse response.
8. Welfare/Farewell Illusion
This is a demonstration of Shepard’s Paradox, an audio illusion synthesized by Jean-Claude Risset. Pairs of chords sound as if they are advancing up the scale, and when looped, it sounds like an auditory equivalent to M. C. Escher’s staircase illusion. What you hear is what you concentrate on hearing. If you want to hear “Welfare” then it is ‘Welfare’ you hear otherwise it’s “Farewell”.
9. Mosquito Sound
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 the 20s” sound as well).
This sound is used by some teenagers as a ringtone on their mobile phones 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, as the noise annoys them. As people get older they lose the ability to hear higher-pitched sounds – that is the reason that only young people can hear this sound – it is too high for most people over the age of 20.
10. Tritone Paradox
The basic pattern that produces this illusion consists of two computer-produced tones that are related by a half-octave. (This interval is called a tritone). When one tone of a pair is played, followed by the second, some people hear an ascending pattern. But other people, on listening to the identical pair of tones, hear a descending pattern instead.
This experience can be particularly astonishing to a group of musicians who are all quite certain of their judgments, and yet disagree completely as to whether such a pair of tones is moving up or down in pitch. This note was once considered to be evil and was not used in music until modern times.
Honorable Mention: The McGurk effect
Did you like our list of the top 10 audio illusions? Which one is your favorite? Let us know in the comments below!