This patch will enable old EAX 4.0 spatial and enhanced audio for Thief Deady Shadows.
Tested on my Realtek ALC295 chipset.

Yes, will work fine with game unofficial patches (Sneaky Mod etc...).

But what is EAX Audio? See YouTube videos like this (reverb is a bit exaggerated in this video IMHO but gives you an idea):

• you should have OpenAL[www.openal.org] already installed...
  
• download latest DSOAL (read below)
  
• copy dsoal-aldrv.dll, dsound.dll, alsoft.ini (you can edit settings*[raw.githubusercontent.com]) to "Thief Deadly Shadows\System\" directory where the T3Main.exe is located
  
• add these keys to the Registry (save the text as a file 'ThiefDSOAL.reg' and double click it to merge it with Registry):
  
  Windows Registry Editor Version 5.00 [HKEY_CURRENT_USER\SOFTWARE\Classes\CLSID\{47D4D946-62E8-11CF-93BC-444553540000}] [HKEY_CURRENT_USER\SOFTWARE\Classes\CLSID\{47D4D946-62E8-11CF-93BC-444553540000}\InprocServer32] @="dsound.dll" [HKEY_CURRENT_USER\SOFTWARE\Classes\CLSID\{3901CC3F-84B5-4FA4-BA35-AA8172B8A09B}] [HKEY_CURRENT_USER\SOFTWARE\Classes\CLSID\{3901CC3F-84B5-4FA4-BA35-AA8172B8A09B}\InprocServer32] @="dsound.dll" [HKEY_CURRENT_USER\SOFTWARE\Classes\WOW6432Node\CLSID\{47D4D946-62E8-11CF-93BC-444553540000}] [HKEY_CURRENT_USER\SOFTWARE\Classes\WOW6432Node\CLSID\{47D4D946-62E8-11CF-93BC-444553540000}\InprocServer32] @="dsound.dll" [HKEY_CURRENT_USER\SOFTWARE\Classes\WOW6432Node\CLSID\{3901CC3F-84B5-4FA4-BA35-AA8172B8A09B}] [HKEY_CURRENT_USER\SOFTWARE\Classes\WOW6432Node\CLSID\{3901CC3F-84B5-4FA4-BA35-AA8172B8A09B}\InprocServer32] @="dsound.dll"

• reboot
  
• enable in-game Options > Audio Hardware Mixing. This will finally unlock EAX Advanced HD and EAX Multiple Environments
  
• if needed, go into your Windows speaker's properties and untick "Allow applications to take exclusive control of this device"
  
  
  That's it. Enjoy! 🎉
  
  
  🔥 LATEST VERSIONS OF DSOAL BUILD 🔥
  
  http://vaporeon.io/hosted/dsoal-builds/
  e.g.:
  
  dsoal-r418a.7z 2021-Feb-23 06:26:09 643.1K application/x-7z-compressed
  Much improved stereo panning, reverb and env-echo!
  
  NOTE: if latest version crashes launching the game, or after it exits to destkop (!), try a different version under the /old directory online

These are the settings I'm using in my alsoft.ini with Realtek ALC295:

boost=<n> controls reverb amplification. You can try 0 (default), +6 (double), -6 (half)... depending on your audio chipset.

Some settings explanations here: https://github.com/kcat/openal-soft/blob/master/alsoftrc.sample

👉🏻 Try first to clean up your system: UNINSTALL OpenAL and any other EAX hack like "Creative ALchemy Universal" (outdated), if previously installed.

After the uninstall of OpenAL and "Creative ALchemy Universal" be sure you don't have OpenAL32.dll in C:\Windows\System32 and SysWOW64 dirs anymore.

Remove from "Thief Deadly Shadows\System\" these files, if any:
⠀dsoal-aldrv.dll
⠀dsound.dll
⠀alsoft.ini
⠀eax.dll
⠀OpenAL32.dll

... Finally, retry this guide from the beginning. This should fix the problem for most users.

After a correct OpenAL (currently 1.1) installation you should have:
‪C:\Windows\System32\OpenAL32.dll (6.14.357.24) (~120KB, this is for x64 games and exes)
‪C:\Windows\SysWOW64\OpenAL32.dll (6.14.357.24) (~106KB, for x32 games and exes)

⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⚠️IMPORTANT⚠️
NEVER run games as admin or in XP compatibility mode etc. This can also interfere with the .dll loading... In our case here, check T3.exe and T3main.exe.

Not recommended but, a few users who reported missing sound, solved their issue using old DSOAL files from https://www.nexusmods.com/newvegas/mods/65094?tab=files
So give it a try if the most recent files in this guide won't work for you and you already experienced problems in other OpenAL games with your audio chipset (you can use HWiNFO to identify your HW).