Mackie C4 modifier buttons in Logic Pro

The four buttons in this area are similar to those found on your computer keyboard (but are independent of the keyboard modifiers). Many Logic Pro functions behave differently when one or more modifier keys are pressed in conjunction with another key or mouse click. This also applies to the C4 control surface.

Here is a generic description of the modifier button functions:

SHIFT: Switches other buttons to an alternate function.
OPTION: While held down, parameters are set to the minimum, default, or maximum value when edited with a V-Pot.
CTRL: Disables the Group function.
CMD/ALT: While held down, parameters are edited in Fine (high-resolution) mode when a V-Pot is turned.

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Control Surfaces Support Guide for Logic Pro

Mackie C4 modifier buttons in Logic Pro