Volume Control

FC

This determines how much the foot controller will affect the overall volume of the sound. This is like the other amplitude-modifying parameters in that in works in the opposite manner than you would expect. My guess is that the TX81Z has a certain maximum amplitude that it can output, so this setting decreases the volume of the pedal's zero point. In other words, the higher the setting is, the lower the volume is when the foot controller is at zero, which effectively gives you more control of the volume.