DESCRIPTION:
A visualization of the Shepard-Risset glissando, a type of Shepard tone.
The Shepard tone is named after Roger Shepard, and is a sound consisting of a superposition of pitches separated by specific intervals. When the fundamentals fade into and out of a frequency range, it creates the illusion of a never-ending descent or ascent in pitch (that does not ultimately go any higher or lower). The varying intensity of the colored lines represents the loudness of the tone at that specific time and frequency. Notice how each diagonal line fades into blackness at its ends. The illusion can be thought of as the auditory equivalent of a barber's pole.

Here, we synthesized the image on screen at 48-tones per octave, fading in from pitch to pitch to create the illusion of continuity. For the three segments, we have: a downwards glissando on the horn centered at 275Hz, an upwards glissando on the triangle wave centered at 330Hz, and a downwards glissando on the triangle wave centered at 330Hz.