Swirling brownface-era harmonic vibrato.
“Leo was right”
The Catalinbread Pareidolia Harmonic Mesmerizer is based on the vibrato found in early 60’s Brownface Fender amplifiers… The big ones like the Twin, Pro and Concert amps featured this unique, yet complex vibrato circuit. These days folks get hung up on Fender’s use of the word Vibrato (frequency modulation) when most Fender amps were actually tremolo (amplitude modulation). But most folks are not actually familiar with THIS particular design. If they were they would realize that the Vibrato in these amps were actually more than Tremolo. I am not sure exactly what the effect should be called. Vibrato? Tremolo? Modulated dual filter? Phasor? Leo called it “vibrato” which isn’t technically correct, but certainly closer and more complex than any of the Fender tremolo circuits that followed. It is an amazing sound!! Truly the “sinewave” Brownface tremolo sound.