D3 used to support Aureal 3-Dimensional sound cards, providing 3D spatial audio. The hardware and drivers is outdated, so all support in code has been removed, including UI mixer setting.
Read more about A3D here: https://en.wikipedia.org/wiki/Aureal_Semiconductor#A3D
Join the license header with historical comments using a separator so IDEs can correctly parse the initial header.
Also use .gitattributes to ensure all files are LF.