Over the years, Fender had three basic designs of tremolo circuit built into its amps and the most aurally intriguing is the 'harmonic tremolo' (based around a dual-band filtering effect) once briefly found in early-60s 'Brownface' amps.
The Pareidolia offers a re-creation, delivered via standard tremolo depth and rate knobs, coupled with a volume knob that hits unity gain at about midway, so can give your amp a nice kick (turn the depth down and you can use it as a pure boost).
An LED pulses in time with rate and intensifies its colour change as depth is increased.
Sound-wise, what you get is tremolo- based but it's not just amplitude (volume) modulation that's goingon here - there are elements of both phasing and pitch modulation, somewhat akin to a Uni-Vibe or rotary speaker, casting a gorgeous otherworldly haze over the tremolo.
