The file containing the settings can be found under /etc/X11/xorg.conf
In order to edit the settings, you shall refer to the tons of docs you can find all over the net about it.
One thing that could help you to create a working configuration is the tool alsaconf. Launch it from a console as root with the command:
/
|
Source code
|
1
|
usr/sbin/alsaconf
|
answer the questions you're prompted for as prcisely as possible. It will create you a new xorg.conf that might be working. Later on, you can tweak the file to improve performance and functionality (read the docs first! And make a backup of a working file, so you will be able to get your settings back if something went wrong).