Based off the "Shepards Tone," and audio illusion of ever rising tone. Interval has to be tuned correctly to make the various peak filters line up. Fading controls how long the fade-in and fade-out time is for each tone.

An endlessly rising series of peak filters. They fade in and out so that, when going slow, it's hard to hear any beginning or end. The effect is that the tone seems to rise forever,