Very freaky audio illusion

[davidrice]

Hi All,

 

Can anyone explain what is happening in this track:

 

http://www.yourfilehost.com/media.php?cat=audio&file=endless.mp3

 

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.

 

Worth your time to listen!

[gsilbers]

FM synthesis maybe?

[David Nahmani]

Naaah.. it's just playing an two notes at an octave interval. On the first sample, you barely hear the low note, but clearly hear the high note. As the notes progress, you hear the low note more and more and the high note less and less. In the end, all you hear is the low note, which becomes the high note from the first chord.

 

If you try to stick with the high note (sing it along for example), you'll realize it totally disappears around the 5th chord or so.