Rotary Sound Processor

Authentic rotary speaker sounds via COSM technology
Slow/Fast transition time is adjustable from gradual to rapid change; optional Expression pedal can control speed in real time
Onboard Overdrive effects
Adjustable mix balance between Treble Rotor and Bass Rotor
4 types of sounds, from standard rotary speaker effects to rock-oriented tones, UNI-V, and more
Guitar/Keyboard switch
Dazzling virtual-rotor display

https://www.boss.info/us/products/rt-20/