Grass Valley DD10 part 1 - Manual (Page 55)

2.8 Operation of the keyer menus Diamond digital DD10
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This method influences both ends of the key area and leaves only one selectable,
average clip value invariant.
CLIP determines that key signal level in the proximity of which linear,
unlimited keying has to be performed (effective only at GAIN > 1).
GAIN determines by gain change the width of the area around
CLIP within which linear, unlimited keying has to be performed.
Clip / Gain