The Shepard’s Tone is an audio illusion in which we seem to hear a constantly rising tone. Much like how the lines on a barbershop pole seem to constantly rise or fall, the tones in the Shepard’s tone seem to rise forever. In reality, there are new tones introduced in the lower regions as the tones in the higher regions extend out of audible range. The average pitch stays the same, but we perceive the scale to be constantly rising into infinity.
There are many examples of the shepard’s tone used in musical compositions before it was even discovered or named. It can create a sense of rising excitement and energy in the music, but can also create an eerie and unsettling tone.
In this musical excerpt from Tchaikovsky’s Symphony No. 6 in B Minor (Pathetique), we can hear an example of the shepard’s tone illusion before it was recognized as such. In the score we can see that only one octave is used in the scale, but when we listen to the music we can hear the illusion that the notes seem to continue above an octave.
(from Leonard Bernstein’s The Infinite Variety of Music)
Passage from Alban Berg’s 1925 opera Wozzeck
“In his 1925 opera Wozzeck, Berg employed a continuously rising scale that was orchestrated in such a way that the upper instruments faded out at the top of their range while the lower instruments faded in at the low end.” (Diana Deutch)