In this video, Stephen Mendes demonstrates a 5U modular synth patch to create a descending Shepard Tone.
Shepard Tones, named after Roger Shepard, are sounds that create the illusion of infinitely ascending or descending pitch. The effect is created by cross-fading between multiple sounds. For example, as a pitch descends, it fades out and is replaced by fading in a higher pitch.
Here’s an example of synthesizing an ascending Shepard Tone.
Someone did this with the Arp Odyssey’s sample and hold https://m.youtube.com/watch?v=-p16EaUQhag
The Kurzweil K250 had such a tone called “endless glissando”. For some reason they never featured it ever again, even when having legacy K250 sounds available for later instruments.
A number of KORG synths (R3, micro, RADIAS) have an “Endless” wave-form built-in that reproduces that effect. I never found much use for it, other than it being an unusual effect. It’s a little like playing the top end of a “mixture” stop on a pipe-organ, these frequently reset every octave as otherwise they’d exceed the human auditory range.
But Hans Zimmer has apparently used the effect extensively in the film “Dunkirk” to sustain the thrill of the action!
Dunkirk / Hans Zimmer use of Shepard town demonstrated here on YouTube:
https://www.youtube.com/watch?v=LVWTQcZbLgY
– even Mario 64! 🙂