a) An effect selected by the PST PTN push-button where a wipe pattern is used. The characteristics of the pattern are set using the pattern controls. If the effect is wiped on-air over an existing onair background, the wipe pattern will only move as far as the limit set by the vertical and horizontal limit controls. This is sometimes called a preset wipe or a wipe to a pattern limit. If the effect is mixed on-air, it is called a mix to a pattern limit. b) The ability to set both horizontal and vertical limits to the size a pattern will grow to when the fader is moved to the B bus.

Ampex switchers can wipe to a preset size, mix in a pattern already at a preset size, and mix or wipe in keys with preset limits. Mixing in a key using preset patterns allows portions of the key to be masked off, and this is the mask key feature on Ampex switchers.