Drag the Key parameter to set a key scale modulation of the panning position. In other words, the played keyboard note position determines the panning position.
Use the Pickup parameter to spread the two pickup signals across the stereo spectrum when both pickups are active (Upper+Lower or Upper-Lower modes).
You can use both spread types at the same time. They are automatically mixed. The ring around the Stereo Spread button graphically displays the effect of both parameters, as follows:
The key scale range is indicated by orange areas in the ring.
The pickup panning position is indicated by red lines in the ring.
In Logic Pro X, vertically drag in the upper (Key) half of the circular Stereo Spread button. The center position is MIDI note number 60 (C3).
Set this parameter to the maximum value for extreme left/right panning (semitones) at MIDI note number 60.
In Logic Pro X, vertically drag in the lower (Pickup) half of the circular button. Higher Pickup values move the signals of both pickups away from the center position—one further to the right and the other further to the left.
Set this parameter to the maximum value for extreme left/right panning.