This patch is for any users that are experiencing lack of audio or other sound issues. IF you do not have these issues, you do not need this patch.
-The original ISO for the first run of disc contains a bug in Microsoft’s DirectX libraries that affect a small minority of users. These users experience a problem in which they get no audio associated with the game.
-The patch modifies the Defense Grid executable file to use the March 2009 version of DirectX and updates the audio content version to remain compatible with that version of DirectX. None of the actual audio assets changed. It will also make sure to install the March 2009 version of DirectX that Defense Grid relies upon.