If you've seen the film Dunkirk, or many other films directed by Christopher Nolan and scored by Hans Zimmer, you've encountered an auditory illusion called the Shepard's Tone. Like an audio version of a Moebius strip or perhaps an M.C. Escher drawing, it creates the perception of a continually rising (or falling) pitch or scale when, in fact, the range of pitch remains constant.
What's really going on is a simple rising or falling series of the same notes, looped indefinitely and layered at least three times. One layer gets louder from beginning to end, the next remains the same in volume, and the next gets quieter. Your ears and brain put it all together as one phenomenon that's moving and yet standing still.
In a cinematic context, this can be used to establish tension or dread, as Nolan and Zimmer often to do great impact. In their flagship Montage synthesizer, Yamaha have captured the Shepard's Tone in the form of the new Spiralizer effect, which is included in firmware version 1.6 and later. This is an effect working in the audio domain (i.e. not some type of synthesis setup), so it can be applied to any layer in a Montage "Performance" (multi-timbral setup) and even to external audio.
Blake Angelos of Yamaha explains and plays the effect in the video below, showing engaging forms of harmonic motion that would at the very least be much more difficult to achieve by other means in a keyboard.