Low-Frequency Compressor, to be exact. Anyone use one? Ever see one? Metal box, three knobs on top, Volume, Tone, and Sustain. Plus a big switch for steppin' on. No external power options. 9-volt batteries only. They're old. Mid 70s, I think. I found one in my dad's garage and got it fixed up...WOW, cool tone. Doesn't sound anything like other compressors I've used, but it's super great. My dad called it his "insta-good tone box." Any note I hit becomes super rounded and nice sounding. Takes a lot of sharpness of the initial tone...Which makes slap not sound good, but fingerstyle so so great... So anyway...Anyone else ever used one of these? This is the only one I've ever seen.