The infinite gamme (auditory illusion)

This illusion is similar to a well known optical illusion: Penrose’s infinite staircase (left).

It is the repetition of the same sound motif, which initiates the sensation of an infinite continuity. The intensity of the middle frequencies is high (yellow), whereas that of the high and low frequencies is low (mauve) (see the figure horizontally).

On the ‘duration’ axis, we can see that the motif repeats itself.
 The association of the repetition of the motif and the spread of the intensity depending on frequency gives the illusion of an infinitely increasing scale, when in fact it is just repeating. However, if you listen carefully, you can tell.