The Buchla 260e generates Shepard-tone auditory illusions — pitches that appear to rise or fall endlessly without net movement

The 260e Barber Pole module uses a duophonic pitch class generator (two oscillators, each simultaneously producing its pitch in all audible octaves) to create Shepard tones. In barber pole mode, an internal computer continuously raises the left oscillator while lowering the right (or vice versa), each wrapped through octaves so no net pitch change occurs globally, but the perception is of endless ascent or descent. The rate is variable up to 2.5 octaves per second and voltage-controllable; pitch intervals between steps are adjustable from quarter-tones to tritones. Shepard tones were first described by Roger Shepard. The 260e also has a continuous mode for paired ascending/descending sweeps.

Examples

Set the 260e to barber pole mode at a slow rate, gate the outputs through a 292e LPG to sculpt dynamics — the listener perceives a constantly rising melodic wash.

Assessment

Explain why the Shepard tone illusion requires multiple simultaneous octaves of the same pitch class. Describe the difference between barber pole and continuous modes on the 260e in terms of what both oscillators do.