Inserting Plugin Effects in GarageBand

First make sure that Audio Units are Enabled for use in GarageBand: Select a track. You'll see the Smart Controls window. Be sure to have access to the Inspector view. GarageBand loads tons of crap insert effects by default. you might want to take that out first. You can then select the Audio Unit of your choice. Voilç! Take note that you're better off tweaking the controls on the actual plugin interface that the few smart controls the try to push on you.