A soundcache is a file that contains the first .125 seconds (125 milliseconds) of each sound required in a map. At level load, Source loads the relevant cache files instead of the sound data itself in order to save memory and decrease waiting times. During gameplay, when a sound is requested, it begins to play immediately while the full sound is asynchronously loaded from the hard drive. In most cases, there is enough data loaded by the time the 125 milliseconds of cache data is exhausted such that the async I/O never needs to "block" gameplay to finish loading. If the async layer, however, does need to block, then a noticeable framerate hitch can occur. These hitches can be displayed to the developer console with the cvar
After an update in 2018,no longer uses soundcaches, and loads all the audio files in real-time instead. This also means that any console commands that used to be associated with it (such as snd_rebuildaudiocache) have been removed.
Re-building the .manifest Files
These instructions apply to mods trying to generate the best possible .cache files:
- Create a text file called
maplist.txtand place it into the game directory.
- Add in all of the map names to
maplist.txt. Just add the map names, e.g. d1_trainstation_01, not d1_trainstation_01.bsp. Separate each map name with a line break.
- In Steam "My Games" Page, right click your mod then select Properties. Open Set Launch options... and enter following line:
-sw -console -condebug -nocrashdialog -makereslists -usereslistfile maplist.txt +mat_picmip 2 +r_lod 3 -autoconfig
- Click OK and run the game. Running this process can take a very long time, and if the engine crashes at any point, the data will not be valid. The engine must make it through the entire
maplist.txtfile cleanly to generate valid .cache files. Don't forget to revert your command line option once it finished.
- Once complete, reset mat_picmip to 0, or its previous value
The engine will run and start each map, wait a few seconds for things to settle, and write out a reslist to the
reslists folder. These reslists are then used to build the actual sound .cache files. At exit, after running with the above command line, the engine should rebuild the meta-cache files and all map specific cache files based on the
mapname.cache is built using the accompanying .manifest files, which contains a list of sounds Precached by that map, as well as the reslist files mentioned above which contain the names of all files accessed during level load, not just those mentioned as Precached.
- .cache files can be viewed with Game Extractor 
- .manifest files can be viewed with any text editor.
_sharedprecache.cache: contains data for precached sounds (see the Precaching Assets section for info about precaching) common to over 50% of maps (e.g., sounds referenced by the response system which can occur in any map are always precached).
_other.cache: contains the file header, but no preload data, for any sound files that were not encountered in any other precache lists. Sounds in this cache will never cause I/O-related blocking as they play back fully asynchronously, that is, they only begin to mix data to the sound hardware after the sound data has completed asynchronous loading.
<mapname>.cache: Contains the remaining files that were Precached by the engine for the specified .bsp, but are not already a part of
_other_rebuild.cache: This is a temporary file used as a way to quickly rebuild the runtime .cache files above.
Although the engine-generated
.manifest files help somewhat, editing the files by hand after their generation can increase performance by some 400%. Look out for '\VO\' files in particular: in mods based on Half-Life 2, there will be three VO entries followed by three Combine soldier death sounds that you will want to keep, followed by hundreds of further, probably unneccesary, VOs that can all be deleted. After deleting all VO entries your manifests (and thus caches) should be under half their original size! This effect can then cascade down and produce more optimised
_sharedprecache files, reducing duplication (in the author's experiment, the engine-generated caches were 30MB while his own were 7MB).
There are further entries that can be deleted, for example weapon sounds for weapons your map does not use, but care should be taken to avoid the deletion of files that will be used, as absent cache entries will likely cause hitches.
You don't have to ship your mod with above caches. If you include reslist/.manifest files, the game will build sound caches when you first run it. However, this process can take a signifigant amount of time and users may be confused and/or get impatient. If your caches are small, you may want to consider shipping them anyway.
- Writes the .manifest file. Possibly buggy and probably not necessary based on using the above-described command line to automatically rebuild the .cache files.
- Rebuilds the .cache files. Only has effect if valid reslists and .manifest files exist.