Amp Recording Studio exclusively uses a variety of UAD Plugins for Tracking and Mixing. UAD-2 Powered Plug-Ins offer warm sonic qualities and character not found in other VST / AU / RTAS plug-ins.

Link to UAD website:

 

http://www.uaudio.com/uad-plugins.html

More Info:

http://www.uaudio.com/blog/uad-2-powered-plug-ins-basics-faq/