Shepard-Risset Glissando Generator.

Press a MIDI note a note to hear the effect.

Use the knob under “LFO Control” labeled “Freq” to adjust the speed range.

Use the red knob under “Manual Control” labeled “LFO Control” to fine-tune and reverse the speed.

I used the “Sine Nine” waveform, but the effect works well with most waveforms.

There’s a pitch shifter at the end of the chain, doubling the effect at 7 semitones above.