Audio “Optical” Illusions

This time “Mighty Optical Illusions” brings you another type of illusion. Audio illusions, also known as Audio Paradoxes are sometimes to be found in nature. The best known audio paradox is known as Shepard’s paradox. It is the audio equivalent of the endless staircase illusion made famous by M. C. Escher. In this audio paradox a series of tones can be made to sound as if they are ascending or descending in pitch forever. You can download these three mp3’s to see what I’m talking about.

The following graph of Shepard’s paradox shows frequency versus time. You can plainly see that the single pitch section appears to be increasing. Note that if the same graph is looped you can see that the finishing pitch is the same as the starting pitch.

It may be obvious to the eye, but the ear cannot perceive where the sample starts and finishes. If you listen to this sample the tones will appear to increase in pitch even if the sample loops back to the beginning and starts over. Here are the Audio Samples. This effect works best if you put on your head-phones. If the players below don’t work for you, download the mp3s, and loop them in your player.

Shepard’s ascending tones (MP3) – 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 (MP3) – 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 (MP3) – 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.

45 Replies to “Audio “Optical” Illusions”

  1. That is very interesting. It hardly seems possible… but then I guess that most of the stuff on this blog hardly seems possible ;)

  2. I only have a few flukes with the audios. i did put the first one on loop and could tell without looking at my player when it stopped and began. The falling bells is easy enough to hear, but the drum beat actually had me stumped! i tried conducting it, but just couldn’t manage to stay at one tempo. overall, i do like these, though. :)

  3. I only have a few flukes with the audios. i did put the first one on loop and could tell without looking at my player when it stopped and began. The falling bells is easy enough to hear, but the drum beat actually had me stumped! i tried conducting it, but just couldn’t manage to stay at one tempo. overall, i do like these, though. :)

  4. i figured out the first two. in both clips, there is not one pitch playing at a time, but two, and they are octaves apart but the same note. as the scale progresses, the top note fades away and another, lower octave fades in on the bottom so that it is the same chord as it was in the beginning.

  5. I could tell when the first started and stopped, I could tell that the second’s pitch got higher, and that the third’s tempo remained the same.


  6. Instead of “Audio “Optical” Illusions”, you should simply call that “Auditive Illusions”. A motorcycle is not called a “motorized bicycle without pedal”.

  7. It seemed weird, but the first one is difficult to work out, but if listened close enough, and keeping the correct pitches in mind, it can be heard, although i think a person with perfect pitch might find this easier. On the second one it is clear to hear it gets higher in pitch, fairly simple to hear. The third one was odd though, although it does stay the same tempo, you just have o count the same beats, and then you can hear it all fit in.

  8. none of the other ones worked.. ( i’m too old for the mosquito one apparently.. and i don’t have headphones for the matchbox one ( i have speakers.. but only ONE works…. go figure) This one however.. tripped me out…

  9. This “illusion” is also apparent in “Closer” by NIN during the chorus (where Trent sings “I want to **** you like an animal”), although the pattern doesn’t progress through a complete scale.

  10. I am having a little trobule downloading the mp3s it will keep loading and never actually load. could you make them into a windows media player file or a real player or quicktime? that might make t easier…. love the illusions I can see, or hear!

  11. Once upon a time I found an interactive flash of this paradox, something like a grey circle with yellow and red dots.
    I found around the net but I lost the link =(
    Anyway I think that J.S.Bach is cited in “Gedel Hescher and Bach” mainly for his “Canone Reale” (I don’t know how is in english, sorry) that contain the same paradox.
    Your site is fantastic and I will end loggin’ in.

  12. try listening to them all at the same time.
    It will be the next hit
    like those NOW pop music compilations.

  13. Brian May of Queen uses the Shepard’s paradox to create an intro & outro guitar piece on Queen’s A Day at the Races album.. The guitar ‘symphony’ appears to be continually going up and up..

    Check it out if you want to hear a version of this that has been put together very seamlessly…

  14. Interesting, but the illusion only works if you have the mp3 on repeat, and you focus on only one scale (the highest note going up or the lowest note going up). If you focus on a different note on the repeat, or if you alternate notes during, the illusion fails.

  15. the third one clearly gets faster. listen to the end tempo then listen to the beginning again than the end again.

  16. the third one definitely gets faster. the drum beat has other beats subdividing it, and at the end it speeds up to twice the original speed, but the beat is somehow set up to sound the same as the starting beet. if you keep looping it, it sounds like it keeps getting faster (which it does) but if you try really hard to hear the slower beat you can do it.
    kinda hard to explain… if you don’t understand me them I’m sorry =\
    incorrect description, but a good illusion nonetheless


  17. I can’t download any audio from this site, so i am unable to see the hear the file that is inaudible to anyone over 20, and this one, and any other ones, is there any other way to download it?

  18. The third one works by emphasizing certain beats. As it progresses the emphases are on more frequent beats.

  19. the drum one is easy, its not changing timing, its just changing rhythm so it sounds like it is speeding up

  20. its basically the destiny of the money we put in our banks: as soon as it’s earned it gets spoiled in fake bonds …so the work must be done all over again…..

  21. The drum is the easiest to “decode”. i followed at the waves on the screen and i realized the only thing changing is the rhythm.

  22. The Shepard’s Tone starts very low and rises up continuously while another tone raises 6 tones below it. The volume of the sounds raise and lower constantly, I figured that out do to research and having redone the idea myself.

    The quickening beat starts off as a 1-an-2-an rhythm, but eventually starts adding more beats in between in order to make it sound like it’s going faster. But it’s adding faster rhythms to it, without changing the tempo.

    Not quite sure how the bell trick works yet. If I had to guess, it’s probably using a similar technique as the Shepard’s tone. One thing I notice is that it continues to pan left and right.

  23. The bells bothered my ears. It was getting louder and faster while the background was getting lower and slower. The Shepards was cool. It kept on getting higher and higher. Then the drums didn’t sound that much like they were speeding up or getting louder.. Well, maybe somewhat speeding up…..

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