The Synth-1 is a totally unique "Reverse Attack Fuzz Wave Generator" from Keeley. I had a TON of fun playing with this pedal. You can use the Volume / Attack in conjunction with the synth, OR on its own, using the blend control. The intensity of the synth is controlled mostly via the large Filter knob, which is a lo-pass filter. When the synth is triggered, it also adds a fuzz / distortion to the tone. Add an expression pedal to dynamically control the filter as well! I found it really inspiring how dynamically the pedal responded to my playing – I was able to trigger the attack (or not) using different combinations of notes and chords. Way, way, way too much fun. Get one!