True 3D Sound for Headphones in Fallout: New Vegas (HRTF mod) - 1.4
It's a little-known fact that Fallout: New Vegas was one of the very last games to support DirectSound3D which was killed off in Vista onwards.
http://satsun.org/audio/
SoundBlaster X-Fi soundcard owners can restore this functionality with Creative ALchemy, which creates a dummy "dsound.dll" in the directory that wraps DS3D calls to OpenAL. The included DSOAL dsound.dll in this mod works under the same principle, only it wraps DS3D calls to the OpenAL Soft API instead so you can get headphone HRTF, 7.0 surround, or up to 3rd order Ambisonics without the need for a dedicated soundcard.

Read this article if you're unfamiliar with how HRTF works.
https://en.wikipedia.org/wiki/Head-related_transfer_function

Video demonstration:
https://www.youtube.com/watch?v=sYgJlTnpJJQ

Complete list of DirectSound3D games here!
https://docs.google.com/document/d/1SyOw7D0H2ecGxzPsCFEFKwupU8LuazUrlkI-gVTpyhc/edit?usp=sharing


: : INSTALLATION: :

1. Extract the files to the \Fallout New Vegas installation directory.
2. This package defaults to 48000Hz by default, so change the relevant values in alsoft.ini from 48000 to 44100 if you want to use this mod with 44100Hz sample rate.
3. Go into your speaker's properties and untick "Allow applications to take exclusive control of this device", then tick "Disable all sound effects" or some variation of that line.
4. Launch the game; you should immediately notice the spatialized sound.
5. If you do NOT hear spatialized sound, follow the instructions listed here:
https://www.indirectsound.com/registryIssues.html

OpenAL Soft will configure itself to match your speaker settings automatically. Make sure you disable any virtual surround sound programs (Windows Sonic, Dolby Atmos, SBX Pro Studio etc.) in order for this mod to work.

: : PERSONALIZED HRTF INSTALLATION (NOT FOR BEGINNERS!): :

The built-in MIT KEMAR HRTF tables in OpenAL Soft are optimized for an "average head" which means it's likely you won't even hear the HRTF that well. The included "HARD_MODE_INSTALLATION.zip" folder contains 52 extra HRTF tables that are personalized for different heads in both 44100Hz and 48000Hz.

1. Watch this video here to determine the correct HRTF tables for you:
https://www.youtube.com/watch?v=VCXQp7swp5k
The correct HRTF table for you should feel as though the sound is actually moving along the back of your head in-between your ears.
2. Unzip the contents of "HARD_MODE_INSTALLATION.zip" to %APPDATA%.
3. Open alsoft.ini and change the following line
"default-hrtf=Built-In 48000hz"
to match the HRTF table you'd rather use. For example, if you want to use IRC_1037 in 44100Hz, then you would set "default-hrtf=irc_1037_44100". Don't add .mhr to the end of the line.

: : HIGHER ORDER AMBISONICS INSTALLATION: :

If you play on a surround setup, you can actually gain enhanced 3D positional audio through OpenAL Soft's Higher Order Ambisonics. It's far superior to the discrete panning of standard surround sound and can be done on as few as 4 speakers.

1. Unzip the contents of "HARD_MODE_INSTALLATION.zip" to %APPDATA%.
2. Open alsoft.ini and add the following lines to the bottom:

[decoder]
quad=C:/Users/YourNameHere/AppData/Roaming/OpenAL/presets/square.ambdec
surround51=C:/Users/YourNameHere/AppData/Roaming/OpenAL/presets/itu5.1.ambdec
surround71=C:/Users/YourNameHere/AppData/Roaming/OpenAL/presets/hexagon.ambdec
hq-mode=true

Replace all instances of "YourNameHere" with your PC's account name.

kcat himself recommends itu5.1-nocenter.ambdec for better left-right positioning on 5.1. There's also 3D7.1.ambdec which can do elevation on 7.1 speakers but requires a specific speaker layout.
https://github.com/kcat/openal-soft/commit/80c90087984dbd55447f0251937c6d53dbfc22e5


: : 64-BIT BINARIES: :
Over 99% of DirectSound3D games use 32-bit binaries, but Far Cry 1, Crysis 1, and Crysis: Warhead all have 64-bit binaries available. You can use these to try and get True 3D Sound in these games, though compatibility is inconsistent between PCs.

: : FIX FOR INVERTED AXIS: :
Some games, notably Grand Theft Auto: San Andreas, have either an inverted X, Y, or Z axis in the 3D sound calculation. You can force OpenAL Soft to invert these channels globally to fix these specific games. Just go into the alsoft.ini and change the relevant lines from "false" to "true".

: : UNINSTALLING: : 
Remove "dsound.dll", "dsoal-aldrv.dll", and "alsoft.ini" from the \Fallout New Vegas directory.


: : FREQUENTLY ASKED QUESTIONS: :
"I'm getting muffled sound in-game!"
This seems to be caused by Windows 8 and 10's audio stack. Go into your speaker properies and tick "Disable all sound effects" under Enhancements. Then, untick "All applications to take exclusive control" under Advanced. Thanks to toscanini for this.
https://answers.microsoft.com/en-us/windows/forum/windows_10-other_settings-winpc/sound-is-muffled-is-there-a-fix/f8b5cf9c-3347-4036-b1a5-7dff5b1da487

"I'm still not getting 3D sound even after following step 5!"
You might need to look for an unlocked version of Creative ALchemy and boot up the game with it once, then reinstall DSOAL. I cannot provide you with this due to the Terms of Service.

"My sound is cutting out in Tales of Two Wastelands!"
Go into alsoft.ini and change sources=256 to sources=1024.
(Verified by "DeathWrench" and "redmaxblower" of NexusMods.)

"I don't hear any voice modulation effects with power armor or intercoms!"
This is a known bug, unfortunately. DSOAL does not currently support the DirectX 8 effects that Fallout: New Vegas uses for these, it only supports EAX 1.0 through 4.0.

"I installed this mod but I don't get any sound in-game!"
Make sure your speaker settings match what's set in alsoft.ini. If you want to use 48000Hz sound output, change it to "frequency=48000Hz" and "default-hrtf=Built-In 48000hz" in alsoft.ini.

"Will this mod affect any other mods that are already installed?"
No, as long as those mods don't use dsound.dll in any way.

"Are there any more config tweaks for alsoft.ini?"
Yes, there is a full list here.
https://github.com/kcat/openal-soft/blob/master/alsoftrc.sample

"The EAX reverb is too loud in ___! How do I fix this?"
Unfortunately, DSOAL has a bug where it doubles or sometimes quadruples reverb sends when HRTF is active at the same time.
https://www.youtube.com/watch?v=Q4_NjSIQswA
The only fix is to adjust the boost= parameter until it sounds right. boost=-6 corresponds to half volume and boost=-12 is quarter volume. 

"When I use the error log .bat, I get a message saying Panning for multi-channel buffers is not supported."
This is a false flag, don't worry about it.


: : CHANGELOG: :
v1.4
-Updated with latest DSOAL build (thanks mrpenguinb) and OpenAL Soft 1.22.2 stable build:
	-EAX effects are now more accurate to real hardware levels.
	-Games that were previously only compatible with DSOAL v1.1 will now work properly.
	-It is now possible to force inverted X, Y, or Z-axis globally to fix games like GTA:SA.
	-Optional 64-bit binaries are included for Far Cry 1, Crysis 1, and Crysis: Warhead.

v1.31a
-Minor update with small bugfixes, OpenAL Soft 1.19.1 stable build, 48000Hz HRTF presets, and new instructions for activating 3rd Order Ambisonics on surround setups.

v1.31
-Updated with latest DSOAL build that fixes EAX 2.0 occlusion in compatible games.

v1.3
-Updated with latest DSOAL and OpenAL Soft builds that includes the following:
    -Support for EAX 3.0 and 4.0 in select games (not Fallout: New Vegas)
    -Increased number of compatible games.

v1.2
-Updated with latest DSOAL build that includes the following fixes:
    -Sounds (like reloading) that should play centered now correctly play centered.
    -Support for error logs (use the included .bat files).
    -Volume rolloff now works correctly in older games that were affected.
    -Full compatibility with EAX 2.0 reverb, occlusion, and obstruction effects.
    -Reverb sends now play EAX 2.0 reverb at the proper volume.
    -Improved compatibility with A3D-to-DS3D wrappers in games from 1998-2000.
    -Partial EAX 1.0 support for games that don't use DS3D unless EAX 1.0 is on.
-Added 52 extra HRTF tables in a separate .zip folder to make Hard Mode Installation much more streamlined.

v1.1
-Updated with latest DSOAL build and reconfigured settings to hopefully fix any problems people might be having with distorted sound and audio cutting out.

v1.0
-Updated with latest DSOAL and OpenAL Soft .DLLs.
    -Removed older DSOAL source and other files to greatly trim down on file size.


: : LEGAL: : 
DSOAL and OpenAL Soft are licensed under LGPL. They were created by kcat (Huleed).
https://openal-soft.org/
http://repo.or.cz/dsound-openal.git
https://www.gnu.org/licenses/lgpl-3.0.en.html#content

The .mhr files in this collection were processed from the following, freely-available sources with no restrictions as long as the following authors are cited:

MIT KEMAR tables copyrighted 1994 by MIT Media Laboratory;
Bill Gardner (billg@media.mit.edu) and Keith Martin (kdm@media.mit.edu)
http://sound.media.mit.edu/resources/KEMAR.html

CIAIR tables copyright 1999 by Itakura Laboratory and the Center for Integrated Acoustic Information Research (CIAIR) of Nagoya University;
Fumitada Itakura, Kazuya Takeda, Mikio Ikeda, Shoji Kajita, and Takanori Nishino.
http://www.sp.m.is.nagoya-u.ac.jp/HRTF/database.html

Contact for the IRCAM Listen HRTF Database:
Olivier Warusfel (olivier.warusfel@ircam.fr)
Room Acoustics Team, IRCAM
1, place Igor Stravinsky
75004 PARIS, France
http://recherche.ircam.fr/equipes/salles/listen/index.html


 : : CREDITS: :
http://fallout.wikia.com/wiki/File:Fallout_NV_logo.png
(Credit to Porter21. Use of this logo falls under fair use laws.)
https://i.imgur.com/gXIDw4j.jpg
(Original creator unknown. Use of this image falls under fair use laws.)
https://gaming.si/wp-content/uploads/2017/11/422974.jpg
(Use of this promotional art falls under fair use laws.)