Ooh, I wonder if you could make a Shepard Tone [1]

(I know nothing of music theory so I don't know how to implement it in ToneMatrix's scale)

Edit: it appears making a Shepard Tone requires volume control of each sequence, which ToneMatrix cannot do.

[1] https://en.wikipedia.org/wiki/Shepard_tone

The original ToneMatrix was in turn a knockoff of the Yamaha Tenori-on, which was actually a hardware product - a really pretty sophisticated if sometimes frustratingly limited self-contained controller/sequencer/synthesizer.

Yamaha stopped making the hardware somewhere in the early 2010s, but released a couple of iOS software versions (TNR-i, emulating the original Tenori-on sounds, and later TNR-e which changed the sounds to be more EDM and less... Yamaha).

Inevitably, as software is an eternal treadmill, Yamaha never bothered to update the apps past iOS 13 - but my TNR-W hardware still does the thing, much to the delight of my kids. (I bought one on a whim when my eldest was a toddler - it has survived 10 years of her and then her younger sister's bashing. They're teenagers now! Yamaha makes quality stuff when they feel like it.)

While it never set the world on fire, it also sold enough that used models are still around. If you do buy a used one, note that the original model with the metal case and white LEDs (TNR-W) are worth the premium over the newer white case/orange LED (TNR-O) models; the former are sturdier, have lights on both sides, and can run on AA batteries (TNR-O requires external power).

I remember having a .swf of this 20+ years ago. I wonder if I still have that somewhere on my computer.