El Capitan, FCPX, Audio Units and getting back to normal

Early adopters to El Capitan (OSX 10.11) got off to a rocky start when many third party AUs would not validate. Some people resorted to going back to the Auvaltool from Yosemite to resolve the issue. For the rest of us who hung on for an update to valid software, this is for you.

Description:

First launch of FCPX after upgrade to El Capitan results in crashed auvaltool (unix level validation tool for Audio Units.) Some experience an FCPX that will not launch at all (by all appearances, since Auvaltool does not display any feedback on the screen.) Getting past this first launch requires Force Quitting out of all instances of 'auvaltool' that get launched (I experienced three instances launching.) It takes several subsequent launches of FCPX to "stabilize" the launch situation. We are left with an annoying dialog to deal with to complete the launch:

Three weeks later: OSX 10.11.1 is released. It fixes the AU validation problem BUT we still get the above dialog when launching FCPX.

Solution:

Go to Macintosh HD > Users > YourUserFolder > Library (no longer hidden!) > Preferences

Find the file 'com.apple.audio.infoHelper.plist' and throw it in the trash

Relaunch FCPX. FCPX will revalidate AUs — they all should pass now.

That should get you back to normal 😉

Thanks to Jari Innanen from http://soundwise.fi for helping me find this solution. [I also subsequently found it on fcp.co and the original source was Applecare and Waves support.]