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Audio Modulator

A script that increase the range of which the weapon firing sound's pitch and volume shift (increase the sound randomness, basically) So instead of rifle go brrrrrrrr it will go ↗↘↗↘↗↘↗↘↗↘ instead


Instead of just having one same firing sound, you can have multiple of them, enriching the gun battle experience.
Look into the vpk's scripts folder, open module7.txt
Add new sound variants like below for the weapon firing sound you want

"AutoShotgun.Fire"
{
"channel" "CHAN_WEAPON"
"soundlevel" "SNDLVL_TALKING"
"volume" "0.75,1"
"pitch" "88,120"
"rndwave" {
"wave" ")weapons/auto_shotgun/gunfire/auto_shotgun_fire_1.wav"
"wave" ")weapons/auto_shotgun/gunfire/auto_shotgun_fire_2.wav"
"wave" ")weapons/auto_shotgun/gunfire/auto_shotgun_fire_3.wav"
}
}

This will tell the game to pick randomly between auto_shotgun_fire_1, 2 and 3 when you fire the weapon

However by adding new sound you'll need to build audio cache for it, so place the new sound Left4Dead2/hl2/sound/weapons
Next, start the game and open the console, type "snd_buildsoundcachefordirectory ../hl2/"
This will build the audio cache for newly added sound files. Without this the new sound wont play in game

There is a more complex method that work on any map instead of just Valve's campaign here: https://www.reddit.com/r/SourceEngine/comments/ro322t/how_to_change_sound_script_for_left_4_dead_2/