Previously, you had either a Dolby Digital
or DTS track on your DVD disc's and any DVD with a 5.1 soundtrack was considered top of the line.
But then came High Definition DVD's such as HD-DVD
. Audio became alittle more in depth and complicated with these 2 new HD formats.
There is True HD, Dolby Digital Plus, DTS-HD, and now 7.1 Surround Sound.