In GarageBand, you can define and modify preferences that apply to all projects. You do this in the Preferences window. These preferences are automatically saved whenever you quit the application. A general preference file, named com.apple.garageband10.plist, is found in the ~/Library/Preferences folder. You can’t edit this file directly. Any changes must be made in GarageBand. If you delete a preference file, a new one is created the next time you open GarageBand. All preferences will be reset to their default values.
Choose GarageBand > Preferences or press Command-Comma, then click the name of the pane to open it.