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PAS is a kind of bounding-box for Player or NPC AI sound detection. [Clarify] It is measured as the set visleafs which are audible from the visleaf occupied by the Sensing NPC or Player. [Clarify] Similar to PVS, A PAS-test is only the first filter that a sound must pass in order to be audible to the NPC. [Clarify] (note: PAS is referred to in BSP compile log).