Mutations (1969)
AI & Code
Jean-Claude Risset showed that a computer can deceive the ear. The tone that falls endlessly but never gets lower was the invention of psychologist Roger Shepard — Risset took the steps out of the illusion and made the fall continuous. Digital technology opened the door to a world of acoustic illusions.
Full text
Jean-Claude Risset, being a physicist, used the computer to synthesize sounds impossible in the physical world. In 'Mutations,' he implements an effect known as the 'Shepard-Risset tone' (an acoustic analog of the Penrose stairs).
The computer generates a sound consisting of many octave layers. As the overall pitch slides down, the upper layers smoothly fade out, while new ones imperceptibly appear from below. To the ear, it seems the sound is falling infinitely, even though it remains in the same frequency range. This was a demonstration that digital synthesis is the creation of perceptual illusions.