GarageBand for Mac: GarageBand preferences overview
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.
Open GarageBand preferences
Choose GarageBand > Preferences or press Command-Comma, then click the name of the pane to open it.