The comb room effect combines a dual delay (room circuit) and a comb filter to make echo/reverb-type sounds and resonant feedback. The comb filter is in the feedback path of the delays. An envelope follower gives movement to either the comb filter or the room circuit. The comb resonance control in conjunction with the comb return control can create self oscillation. The preamp for the 1/4” input has selectable gain of 10x or 40x and a soft clipping characteristic. The comb and room circuits are both built around 1 bit delta-sigma converters. In the case of the delays, the analog to digital conversion is done in the PT2399 echo IC. The comb filter uses a simple and gritty A/D converter built of logic chips and op-amps. Which gives the filter a characteristic sound. Clock noise can be heard at lower frequency settings. Patching the room output to the return will bypass feedback through the filter, allowing all frequencies to echo.