Also curious if used or new pedal. If used I'd start with a factory reset. The default presets weren't hard for me to start playing with at all with a little reading of the manual and I think maybe there was a card that described the function of the alt switch.
If you haven't you should probably read the manual, it's 48 pages long but really not much trouble to skim through the important parts.
The input and mix knob both have dual functions, when you press the "alt" button on the back of the pedal the light will flash, and the input knob will be the "sensitivity" knob and the mix knob will be the volume output.
Ideally you want to calibrate your input for the processor, you adjust this based on how hot your pickups are.
And then it's sensitivity you want to adjust to determine triggers based on your playing dynamics.
From the manual ([Invalid or Expired Link Removed])
o INPUT CALIBRATION FUNCTION: We have provided a unique Input Calibration Function to assure that you are getting the best possible interaction between your instrument and the C4. The Calibration process is as follows: 1. Turn the INPUT knob all the way down. 2. Continuously pluck your instrument at your average plucking velocity. 3. Slowly turn up the INPUT knob up until the center LED starts flashing red. This flashing indicates that you have reached the optimum INPUT level. Leave the knob where it is – the process is complete.
• SENSITIVITY (Secondary Parameter). Adjusts how reactive the envelope filter is to the incoming signal. If you like to play hard, but still want a smoother more relaxed envelope filter, you should turn down the SENSITIVITY. For a sharper response to lighter playing, turn up the SENSITIVITY.
And personally I think just about all of the effects become bass worthy effects once you start playing with the mix knob and letting the dry signal handle the low end, well other than some of the iconic OC-2 sounds.
Once you have that all sorted, use the alt button + mix knob to set the volume to be equal to your clean signal with the pedal of, or maybe slightly boosted up to you.
Then if you're like me you'll lose an hour of your day every time you sit down to mess with it