well i can give you my best guess , i never saw any Bis documentation for a2 ( like all thing i think we must wait till after A:o for official info
makes good buisness sense to me) .
soundVehiclePlate1[] = {"ca\sounds\weapons\hits\hit_vehicle_plate_01", 0.562341, 1, 90};
first is volume or DB of the original recording 1 is as recorded your value is 0.5 so half original
second is pitch or speed
third ( guess) the distance from impact that the sound will be heard Max ( or distance at which some fuziness/fade is applied) i say the last because shells have a last figure of 1800 and the sound is different although 1800 may not mean make fuzzy like i said , it may simply be the max distance it will be heard from source.