Finding Audio Units plug-ins on your computer
Audio Units are plug-ins that can be used to process audio by applications such as Logic Pro, Logic Express, Soundtrack Pro, GarageBand, and others. All Mac computers include a collection of Apple Audio Units, and many other manufacturers distribute plug-ins in Audio Units format.
The Apple Audio Units plug-ins are built into the operating system and do not appear as discrete files. Plug-ins from other manufacturers appear as individual components on your hard disk. They may be found in two places:
~/Library/Audio/Plug-Ins/Components ("~" represents your home directory.)
Plug-ins installed in /Library are available to all users on the computer, whereas plug-ins installed to ~/Library are only available to the user in whose home folder they reside.
Note: Some Audio Units will work from either location and some need to be in one or the other. Check with the manufacturer for information on the preferred location for specific plug-ins.