When you play a sound via the "sound" command, it will create a "broadcasted" sound, which is technically hearable all over the level. If an entity is close enough to where the sound originated from then the "noiseheard" condition will be true. Remember that any physics created sounds are also broadcasted, as are footsteps and firing a weapon.
The parameter seems to have no effect whatsoever on this command.
The way it works is if the broadcasted sound's strength, multiplied by 10, is greater than the vector distance from the entity to the sounds origination.... then the sound can be heard by that entity and will trigger the "noiseheard" command.
Hope that all made sense.
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