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Soundscripts contain "sound entries" that are used to wrap Source Source-specific playback instructions around WAV or MP3 files.

File format

Sound entry

A sound entry can define the meaning of a sound to NPCs, its pitch and volume, how far away it can be heard from (attenuation), and can be used to randomise which precise sound file is played. Operator stacks (in all games since Portal 2) can be used to define even more complex behaviours.

Soundscripts are loaded on the server only from:

  • scripts/game_sounds_manifest.txt
  • maps/<mapname>_level_sounds.txt (not in Counter-Strike: Global Offensive)

All filepaths within a soundscript are relative to the <game>/sound/ folder.

    channel    CHAN_AUTO
    volume     VOL_NORM
    pitch      PITCH_NORM
    soundlevel SNDLVL_NORM
    wave       common/null.wav

If a value has a space or tab character within it, wrap it in "quote marks".

Tip.pngTip:To have a random numeric value chosen every time the sound plays, type a lower bound and a higher bound, separated by a comma. Example: volume 0.45,0.65.


Wave / rndwave

Filename of the sound to play.

wave common/blah1.wav

You can also have the engine pick from a list of random files. A given sound won't repeat until all of the others have played. Note that the random choice is decided by the server, not the client.

    wave common/blah1.wav
    wave common/blah2.wav
    wave common/blah3.wav
Note.pngNote:The sound file MUST be in a folder within the sounds folder. So (sound/)folder/sound.wav will work, while (sound/)sound.wav will not.


A number between 0 and 1, where 1 is the sound's original volume. VOL_NORM will insert your mod's default volume, which will probably be 1.


Any number between 0 and 255, where 100 is the sound's original pitch and 255 is very high.

  • PITCH_LOW = 95
  • PITCH_HIGH = 120


Channels are used to categorize sounds in a way that NPCs, and game logic in general, can understand.

Confirm:There is a limit of 256 channels total: 224 Static, 32 Dynamic that can play at any given time.
Exceeding this will result in a channel allocation error, preventing sounds from playing.
Default, generic channel.
Player and NPC weapons.
Voiceover dialogue. Used for regular voice lines, etc.
Note.pngNote:If sound with this channel is emit by an entity that has the "mouth" attachment, the sound comes from it.
Additional voice channel. Used in Team Fortress 2 for the announcer.
Generic physics impact sounds, health/suit chargers, +use sounds.
Clothing, ragdoll impacts, footsteps, knocking/pounding/punching etc.
Sounds that can be delayed by an async load, i.e. aren't responses to particular events.
Confirm:This won't make the sound actually stream; use the * prefix for that.
Used when playing sounds through console commands.
A constant/background sound that doesn't require any reaction.
Network voice data (online voice communications)
Custom channels can be defined here (Allocates a channel for the desire sound entry).


The sound's attenuation; how fast it drops away. The engine starts running into trouble below 60dB.

The following list contains all default sound levels, their attenuation value, real world examples, and in-game examples. All values and real world examples were taken from soundflags.h.

It is possible to pass a literal number value ("150" as opposed to "SNDLVL_150") and freely choose any number between 0 and 255. Games tested: Half-Life 2 Half-Life 2: Episode One Half-Life 2: Episode Two Portal 2

Code Attenuation Value Real World In Game
SNDLVL_NONE 0 Everywhere Left 4 Dead 2: Music disconnected from environment (Ex: checkpoint music, credit music, mob music)
SNDLVL_20dB Rustling leaves
SNDLVL_25dB Whispering
SNDLVL_30dB Library, dishwasher
SNDLVL_40dB Moderate rainfall
SNDLVL_45dB Refrigerator
SNDLVL_50dB 3.9 Average home, heavy rainfall
SNDLVL_55dB 3.0 Left 4 Dead 2: Digital alarm clock in C8M1_Apartment.
2.0 Normal conversation, clothes dryer
SNDLVL_65dB 1.5 Washing machine, dishwasher
SNDLVL_70dB 1.0 Car, vacuum cleaner, mixer, electric sewing machine Left 4 Dead 2: Moustachio whack smash and pop-up, tv static, whacked piano
0.8 Busy traffic Left 4 Dead 2: Various doors, swarm of flies, Lilpeanut audible, bullet impact on wood.
SNDLVL_80dB 0.7 Mini-bike, alarm clock, noisy restaurant, office tabulator, outboard motor, passing snowmobile, police siren Left 4 Dead 2: Jukebox, music spitter spit pile as source.
SNDLVL_TALKING Valve's chosen dialogue attenuation
SNDLVL_85dB 0.6 Average factory, electric shaver Left 4 Dead 2: Moustachio strength attract, big fire after airliner crash in C11M5_runway
SNDLVL_90dB 0.5 Screaming child, passing motorcycle, convertible ride on freeway, hair dryer Left 4 Dead 2: Moustachio strength attract, gas can bursting
SNDLVL_95dB Left 4 Dead 2: Mounted Machine Gun
SNDLVL_100dB 0.4 Subway train, diesel truck, woodworking shop, pneumatic drill, boiler shop, jackhammer Left 4 Dead 2: Music coop player in danger AKA tags (ledge hanging, pinned down by SI), Elevators.
SNDLVL_105dB Helicopter, power mower
SNDLVL_110dB Snowmobile (drivers seat), inboard motorboat, sandblasting, chainsaw Left 4 Dead 2: Boomer alert close, Van in C11M4_Terminal.
SNDLVL_120dB Car horn, propeller aircraft, concert Left 4 Dead 2: Boomer alert, Indoor fire in C1M1_Hotel, Fireworks in C2M5_Concert, Rain in "Hard Rain" campaign.
SNDLVL_125dB Left 4 Dead 2: Boomer alert far
SNDLVL_130dB Air raid siren, fireworks Left 4 Dead 2: Carousel music during crescendo event, C5M2_park perimeter alarm.
SNDLVL_GUNFIRE 0.27 Threshold of pain, gunshot, jet engine
SNDLVL_140dB 0.2 Airplane taking off, jackhammer Left 4 Dead 2: Flock of crows, Lowering bridge in C5m5_Bridge, APC engine.
SNDLVL_145dB Left 4 Dead 2: Wandering witch music ("lost little witch")
SNDLVL_150dB 0.2 Smithing hammer Left 4 Dead 2: Concert music, parade music, zombie choir, Boat Horn
SNDLVL_180dB Rocket launching

Operator stacks

Portal 2 engine branch introduced Operator Stacks, which are used to add complex behaviour to sounds. To enable them, you must set soundentry_version to 2.

There are three types of stack, each triggered at different times:

  • prestart_stack
  • start_stack
  • update_stack
  • stop_stack

In each case you can either start from scratch or use the import_stack command to extend a template defined in scripts/sound_operator_stacks.txt.


	channel		CHAN_AUTO
	soundlevel	SNDLVL_105db
	volume		1.0
		wave		"vfx/light_flicker/light_flicker_end_01.wav"
		wave		"vfx/light_flicker/light_flicker_end_02.wav"
		wave		"vfx/light_flicker/light_flicker_end_03.wav"
		wave		"vfx/light_flicker/light_flicker_end_04.wav"

	soundentry_version 2

		start_stack // applied when the sound begins
			import_stack 	"P2_exclusion_time_blocker_start" // defined in scripts/sound_operator_stacks.txt

			// We are now extending/configuring P2_exclusion_time_blocker_start

			block_entries // prevents another sound from playing
				input_duration 0.25 // seconds to block for
				match_entry "World.LightFlickerEnd" // the sound entry to block
				match_entity false // only on the same entity that this sound is playing from?


There are 28 operators used in Portal 2, but they are re-configured and combined in hundreds of different ways. Most of the resulting "stacks" are very specific, and this page will only deal with the more general ones.

Blank image.pngTodo: Work out a sane way of documenting all this!

Limits the maximum number of sounds that can be played at once, either by sound name or entity. A sound will not stop itself from playing.

import_stack	"P2_poly_limiting_start"

	match_entry "VFX.OGSignFlicker"
	input_max_entries 3.000000

Smoothly transitions a sound from one location to up to eight others as the player moves through a map. An unreleased tool can auto-generate these. Position 1 is where the sound was emitted from.

Confirm:The tool mentioned above may be in the files of Dino D-Day Dino D-Day.
import_stack "p2_update_dialog_spatial_cave"

	input_entry_count 3
	// position 2
	input_position_1[0]	2129
	input_position_1[1]	-850
	input_position_1[2]	-1267
	// position 3
	input_position_2[0]	1473
	input_position_2[1]	-1200
	input_position_2[2]	-1343

Plays another sound entry.

import_stack "stop_and_play"

	entry_name VFX.FizzlerDestroy

Games that support Sound Operator Stacks

Valve Games
Third Party Games

Sound Characters

The first two characters of a WAV's name are scanned for the following:

Streams from the disc, get flushed soon after. Use for one-off dialogue files or non-looping music.
Bypasses DSP and affected by the user's music volume setting (snd_musicvolume). The latter part also requires the sound to be non directional (soundlevel of 0).
Warning.pngWarning: Using this character on a sound entry utilizing an update_stack where the volume is zeroed out, whether by the update_stack or by the sound entry itself(volume 0.0), will cause an update_stack loop. Not only does this have negative performance implications, the sound will consume an audio channel until the loop is interrupted or the sound is stopped. [confirm]
Non-directional sound; plays "everywhere", similar to SNDLVL_NONE, except it fades with distance from its source based on its sound level.
Doppler encoded stereo: left for heading towards the listener and right for heading away.
Stereo with direction: left channel for front facing, right channel for rear facing. Mixed based on listener's direction.
Blank image.pngTodo: Relationship with CHAR_DIRSTEREO in Counter-Strike: Global Offensive Counter-Strike: Global Offensive?
Distance-variant stereo. Left channel is close, right channel is far. Transition distance is hard-coded; see below.
Spatializes both channels, allowing them to be placed at specific locations within the world; see below.
Note.pngNote:Sometimes "(" must be used instead; see below.
Forces low quality, non-interpolated pitch shift.
$ - CHAR_CRITICAL (removed since Source 2007)
Forces sound to be cached at a fixed point in memory. Only affects Original Xbox Original Xbox, which streams all audio regardless of * unless marked as critical.
! - CHAR_SENTENCE (in all games since Source 2009)
An NPC sentence.
Voice chat data. You shouldn't ever need to use this.
& - CHAR_HRTF_FORCE (only in Counter-Strike: Global Offensive)
Indicates wav should use HRTF spatialization for all entities (including owners).
~ - CHAR_HRTF (only in Counter-Strike: Global Offensive)
Indicates wav should use HRTF spatialization for non-owners.
` - CHAR_HRTF_BLEND (only in Counter-Strike: Global Offensive)
Indicates wav should use HRTF spatialization for non-owners, blended with stereo for sounds sufficiently close.
+ - CHAR_RADIO (only in Counter-Strike: Global Offensive)
Indicates a 'radio' sound -- should be played without spatialization
( - CHAR_DIRSTEREO (only in Counter-Strike: Global Offensive)(only in Left 4 Dead 2)
Indicates directional stereo wav (like doppler)
$ - CHAR_SUBTITLED (only in Counter-Strike: Global Offensive)
Indicates the subtitles are forced
% - CHAR_MUSIC (only in Counter-Strike: Global Offensive)
Indicates main menu music

For example:



Spatial Stereo

Adding ) in front of a stereo sound name in the soundscript such as ")weapons/m4a1/m4_shoot.wav" tells the sound engine that it is a spatialized sound; this allows the sound to emit from a specific location within the world. When not used, stereo sounds play in a fixed 2-channel orientation and cannot be panned to simulate a location. Single-channel files do not require ) before the filename and will be spatialized automatically.


Soundscapes have special needs. Stereo wave files used in PlayRandom require that ( is placed before the filename. PlayLooping still uses ) but ( will spatialize the two channels separately for an alternate effect; ( sounds more environmental, but the exact nature of this behavior is unknown. Generic soundscripts can sometimes use ( to gain the same stereo spatialization that occurs in PlayLooping.

For example:

wave ")ambient/stereo_alarm.wav" // Typical usage in a standard soundscript

But in soundscapes:

	time		33,68
	volume		.6,1
	pitch		90,105
	position	0
		wave "ambient/mono_siren.wav" // Mono files are always spatialized properly
		wave ")ambient/stereo_alarm.wav" // WRONG; sound will not be spatialized
		wave "(ambient/stereo_siren.wav" // Correct; sound will be spatialized normally
	volume		.6
	pitch		100
	position	0
	wave		")ambient/stereo_siren.wav" // standard spatialization; both channels originate at same location
	//wave		"(ambient/stereo_siren.wav" // stereo spatialization; one of the channels is spatialized alternatively

Distance variance in Source

Adding ^ in front of a sound name, such as ^weapons/explode3.wav tells the sound engine that it is a distance based sound. The left channel of the sound file is the 'near' sound that will play when the sound originates close to you, and the right channel is the 'far' sound that will play when the sound originates far from you. If the ^ mark is not used in the soundscript, the sound is treated as stereo with no directionality or distance. This is a different feature than the sndlvl entry to control attenuation. This distant variant feature allows you to play two different sounds (but using only one file) and cross-fading between the two depending on how far away the sound originates.

The fade distances are hardcoded to begin at 240 world units and end at 1320 world units, and cannot be changed in custom maps or mods.

See also

  • src/public/soundflags.h
  • src/public/soundchars.h
  • scripts/game_sounds_header.txt
  • scripts/game_sounds.txt