BFR - BFR is a no holds barred, big, f____, reverb. This is more than a giant arena reverb. It's a hall-esque reverb with rich and lush decay in a vast cavern filled with choirs of angels.
X knob controls the amount of diffusion applied to the multi-tap delays used to form the program. At lower X settings, you'll hear these delays bouncing around for a more textured sound. As you increase the X knob, the delays are diffused, creating a smooth texture, and lifting your riffs and chords into the atmosphere. See ya.
X knob controls the amount of the wind and shimmer elements in the Air program. At zero the effect will be off. Turning clockwise will increase the volume of the air effect.