of frequencies that seems to increase or decrease forever, getting higher

and higher like the audio version of the barber pole effect. In actuality new frequencies

are sneaking in the lower range and the higher frequencies fade out of audible range so the

average frequency stays the same even though it seems to rise forever

A single shepard tone is a note made of frequencies an octave apart. Our brains perceive this

collection of frequencies as a single note with a particular pitch, but there's no way

for the brain to tell what octave that pitch is in because it contains all of the octaves.

Multiple shepard tones are often heard in harmony together, such as in this dark creepy

minor chord that goes down, down, down, down, down...

Random shepard tones wouldn't create an illusion, but when two are near each other we percieve

a relationship, chunking bits of information over time and across frequencies into one

perceptual unit that usually lives in the flat topology of pitch space with its absolute

higher and lower, but when you loop the notes into a circle of pitch classes you change

the topology.

Or instead of looping every octave we could loop tighter, into an augmented, augmented

ah....

We can use this effect in a less strict way in our music compositions to create an effect

of ever rising, ever rising joy...