Download additional sounds and loops
After you install GarageBand on your computer, additional content—including patches, drummers, and Apple Loops—may be available.
Some additional content may be needed to perform certain tasks. In these instances, a dialog appears, informing you that additional content is needed, and asking if you want to download it.
Download additional sounds and loops
Choose GarageBand > Download More Sounds.
In the dialog, click Download Now.