A patch contains the instrument, effects, and other settings that control the sound of a track. When you choose a patch, those settings are applied to the currently selected track. You can try a different sound for the track by choosing a different patch, as long as the patch is compatible with the track type.
You can choose a patch in the Library when you create a track, and choose a different patch at any time while you’re working. The Library always shows available patches for the currently selected track. You can search for patches by name in the Library.
Patches for audio tracks can include default effects settings. Patches for software instrument tracks include an instrument plug-in as well as effects settings.
Note: If you have saved track instruments from a previous version of GarageBand, they appear along with patches when the corresponding track type is selected.