you are probably referring to DVD-Audio, which is completely different from an Audio DVD (which is essentially a DVD-Video with high resolution audio tracks, where the "video" part is reduced to the minimum, like a simple tracklist screen).
However, it is possible to create DVD-Audio, using (professional and expensive) products like e.g. Sonic DVD-Audio Creator:
Sonic DVD-Audio Creator is the world's first, and only, full-specification DVD-Audio authoring workstation. Built on core technology from Matsushita (MEI) , the benchmark standard for DVD compatibility and a long-time technology partner of Sonic, DVD-Audio Creator gives you fast and efficient access to every aspect of the DVD-Audio specification, allowing the speedy creation of pure DVD-Audio, complex DVD-Audio and hybrid DVD-Audio/DVD-Video titles.