Apple Logic Pro 9 - Manual (Page 1166)

To change the bounce extensions
1 Click the Bounce Extensions tab.
2 Enter a new extension name in any of the active fields.
For example, the default left extension “.L” could be renamed to “.Left,” or the left surround
extension “.Ls” could be changed to “.LSurr.” Don’t forget the period before the extension.
If you change your mind, click the Reset Extensions button to revert to default entries.
Note: Changing the extension has no impact on the files—it simply makes them easier
to identify. If you find the defaults clear enough, there’s no need to change them.
Setting the Project Surround Format
You can determine the surround format you want to use for a project in the Audio project
settings. By default, a new project is set to 5.1.
1166 Chapter 39 Working with Surround