Built in a rare vintage audiometer (that looks kinda like an old breadbox - with a retractable front cover). This unit features a parasit studio C19 Databus Drive circuit - a CMOS guitar synthesizer with octave up, octave down features plus sawtooth and square wave modulation and vibrato and phaser modulation. Plus a functional led oscilloscope! It can even generate its own signal. You can find videos on my IG page.