Dark Souls: Prepare to Die Edition Update - 12/20/2012

Dark Souls Patch
The new patch solves the broken stereo downmix issue. Basically: if you weren't using a 5.1 or 7.1 (or similar) speaker configuration, you would miss out on a lot of different sound effects. This update brings those sounds to people with a 2.0 or 2.1 speaker configuration.
It also adds some performance tweaks to make the game a bit less CPU intensive.
If you are using DSFix to increase your frames per second (FPS) limit, then the game will crash on startup unless you updat to the new version of DSFix.
Disabling the DLL (rename it or move it) will stop the crashing, as well, but you might as well just update it.
The changelog / updatelog:
-- Performance enhancements
-- Stereo / Audio fixes
So in conclusion: get the update!
Note that this is not the same patch that is available on Xbox 360 or PlayStation 3 (PS3), which was 1.07