EAX

Creative Technology's Environmental Audio Extensions, also known as EAX, attempted to create more ambiance within video games by more accurately simulating a real-world audio environment.

The release of Windows Vista deprecated the DirectSound3D API on which EAX relied on in 2007, so Creative Technology encouraged the move to OpenAL's EFX.

EFX

EFX is a system in OpenAL that delivers high quality sound reverberation. It is the successor to Creative's Environmental Audio Extensions.

Nuclide offers abstraction for new and old entities relying on digital signal processing.

Entities interacting with EFX

env_sound is most commonly used to change the environmental sound processing of a room/area.

In GoldSrc, it'll specify which enumeration of DSP preset to use for audio playback, in Nuclide however we just map it to a definitions file in the filesystem. See EFX files below.

EFX defintion files

Entities that specify a EFX type, usually want to load one from a file.

Here's an example one, efx/city.efx:

density "1.000000"
diffusion "0.500000"
gain "0.316200"
gain_hf "0.398100"
gain_lf "1.000000"
decay_time "1.490000"
decay_hf_ratio "0.670000"
decay_lf_ratio "1.000000"
reflections_gain "0.073000"
reflections_delay "0.007000"
reflections_pan "0 0 0"
late_reverb_gain "0.142700"
late_reverb_delay "0.011000"
late_reverb_pan "0 0 0"
echo_time "0.250000"
echo_depth "0.000000"
modulation_time "0.250000"
modulation_depth "0.000000"
air_absorbtion_hf "0.994300"
hf_reference "5000.000000"
lf_reference "250.000000"
room_rolloff_factor "0.000000"
decay_limit "1"

Most of the parameters are self explanatory.

Console Variables

With the cvar s_al_debug set to 1 you'll get an overlay of information about which EFX file is currently being used, as well as what every single parameter is set to.

You can refresh EFX definitions with a map restart.

Legacy translation table

This section describes behaviour specific to converting entities from Half-Life based levels into the Nuclide environment.

Here you can see which efx file is responsible for handling a legacy env_sound room-type.

roomtype ID	EFX file
0	efx/default.efx
1	efx/gs_generic.efx
2	efx/gs_metal_s.efx
3	efx/gs_metal_m.efx
4	efx/gs_metal_l.efx
5	efx/gs_tunnel_s.efx
6	efx/gs_tunnel_m.efx
7	efx/gs_tunnel_l.efx
8	efx/gs_chamber_s.efx
9	efx/gs_chamber_m.efx
10	efx/gs_chamber_l.efx
11	efx/gs_bright_s.efx
12	efx/gs_bright_m.efx
13	efx/gs_bright_l.efx
14	efx/gs_water1.efx
15	efx/gs_water2.efx
16	efx/gs_water3.efx
17	efx/gs_concrete_s.efx
18	efx/gs_concrete_m.efx
19	efx/gs_concrete_l.efx
20	efx/gs_big1.efx
21	efx/gs_big2.efx
22	efx/gs_big3.efx
23	efx/gs_cavern_s.efx
24	efx/gs_cavern_m.efx
25	efx/gs_cavern_l.efx
26	efx/gs_weirdo1.efx
27	efx/gs_weirdo2.efx
28	efx/gs_weirdo3.efx