The Panel Focus section, located on the center panel below the display, allows you to choose which of the One’s three synths is currently controlled by the front panel knobs. However, sometimes you may want to control the same parameter across multiple synths. To do this, simply hold down the buttons in the Panel Focus section for each synth layer you want to affect at the same time. This will make the panel active for all the layers that are currently turned on.
Note that whichever synth layer’s button you pressed last (while holding down the others) will be the one whose values are reflected in the display window, and its panel focus button will be brighter than the others. However, any knob you turn will now affect all the layers that are lit up.