Can't find AU Lab on my Mac mini.
I have Xcode installed. Where can I find the program?
With Xcode 4.3, the Lion App Store version, Xcode was unified to a single application. At the same time Apple removed some of the smaller utilities to save space on the download. Some of the utilities can be launched from inside Xcode, others are available as a separate download.
AU Lab is in the package "Audio Tools for Xcode" available in the Downloads for Apple Developers page.