It can happen that the information stored in the shared.xml file is not optimal for the connection which can have a direct impact on sound quality of the conversation. Imaging being routed over half the world to call a friend who is living two blocks away from your location.

Deleting the file shared.xml forces Skype to rebuild that list during the next startup. You need to close Skype first and then head over to the Documents and Settings \Username \Application Data \Skype folder in which the shared.xml file can be found.

Just delete that file and restart Skype. Skype will automatically create a new file with that name in the very same directory. That’s still no guarantee that the Skype sound quality will be any better but it offers a good chance if other reasons like blocked ports, p2p background processes and the like are not reducing the quality.