In the 90s, cognitive scientist Roger Shepard came up with the idea of making endlessly rising (or falling) loops by having overlapping notes of rising pitch with the low notes fading in and the high notes fading out (or vice versa for falling). They became known as "Shepard Tones" https://en.wikipedia.org/wiki/Shepard_tone . French composer Jean-Claude Risset then extended this idea to rhythm, creating the Risset Rhythm that endlessly rises in tempo and pitch (there's a recording on https://en.wikipedia.org/wiki/Jean-Claude_Risset ). His original can be quite baffling, and I've read many very unhelpful descriptions of it. So now that I understand it, let me try to explain:
It's a short drum sample (with a highish note in it) that over a period of about 30 seconds doubles in playback rate (hence tempo and frequency/pitch), but at the same time, a double rate version of itself is fading out and a half rate layer is fading in underneath to become the middle layer when it all repeats (and the middle layer becomes the top layer). You can check this by listening to the note in the sample as it slides up an octave over the 30 seconds. About half way through (depending on your ear/focus), the bottom layer takes over as the dominant groove and the process continues. Risset pushes the effect even further, as over the course of the almost 5 minutes, the bottom layer (fading in underneath) is gradually increasingly delayed, making it seem more and more sluggish and making the double tempo version on top of it seem rushier. By the end it's quite a mess (no offense, Mr. Risset!)
I convergently "discovered" Shepard Tones back when I first started looping in the early 90s (using the "Loop of Silence" https://youtu.be/vgXZKNiEGR0 ) and used them a few years ago when using irrational numbers as delays http://malwebb.com/irrational.html . And I also got into looping the harmonic series http://malwebb.com/triangle.html like a kind of musical Fourier Transform, which I turned into a song http://malwebb.com/HarmonicsMalKyDemo... for my nerdy show Notey and Noisy: A Sound Science Mathemusical http://malwebb.com/notnoi.html .
But in 2019, I was first shown the Risset Rhythm and quickly realised I could use it to create another angle on my harmonic series triangle, which I called Risset/Shepard/Harmonic https://youtu.be/2otKFo79Je0 .