Once you've added loops to your track timeline, you can add and edit their sound effects. The controls for the track effects are located in the information panel on the right side of the GarageBand window.
Select a track that you want to edit and click on the "i" button to open up the right sidebar information panel.
Browse the Effects Options
Click on the Browse tab in the sidebar to view and select the effects options for the track. GarageBand has default effects for tracks depending on what kind of sound it is.
Edit the Effects
Click on the Edit tab to change, edit or modify the effects for the track.
