The Advanced pane contains the following preferences:
Audio Recording Resolution: 24-Bit checkbox: When selected (default), GarageBand can record 24-bit files. When unselected, audio recordings use a resolution of 16-bit.
Auto Normalize: Export projects at full loudness checkbox: When selected (default), GarageBand automatically exports projects at the optimum loudness—that is, the highest volume level at which no distortion occurs. This doesn’t affect the volume level when you play the project in GarageBand—only when you export the project.
Movie Thumbnail Resolution buttons: Allows you to choose between a high (default) or low resolution for movie thumbnails in the Movie track.