Page "Doom 3" Paragraph 25

A week before the game's release, it became known that an agreement to include EAX audio technology in Doom 3 reached by id Software and Creative Labs was heavily influenced by a software patent owned by the latter company.

The patent dealt with a technique for rendering shadows called Carmack's Reverse, which was developed independently by both John Carmack and programmers at Creative Labs.

id Software would have placed themselves under legal liability for using the technique in the finished game, so to defuse the issue, id Software agreed to license Creative Labs sound technologies in exchange for indemnification against lawsuits.