Instructions how to enable 3D spatial audio for 'Unreal Tournament 2004' aka UT2004 aka UT2k4.
Intended to be used with headphones (stereo). Works with any sound card.
The difference should be clearly noticeable as sound becomes out-of-head.
Non-native to game solutions to create 3D spatial audio for headphones is done using only 5.1/7.1 channel output and have no elevation. Having 3D spatial sound directly from audio engine has elevation and is more accurate.
Instructions and a way to find best sounding HRTF are included in 'Readme.txt' inside UT2004-OpenAL-XXXX archive.
UT2004-Vertical-Sounds-OpenAL-HRTF-IRC-1037.mp4
Included OpenAL Soft library files are patched to fix voice chat which does not work with official OpenAL Soft release. Taken from here.