It depends on what they sound like before you EQ them. Again....it just doesn't work like that. You add EQ based on what your ears tell you it needs or doesn't need. It is not determined by some universal EQ technique.
I dont know if you're making a joke or not, but if you're not, then, ad libs ARE for recording. They are your background vocals that usually add a sense of energy and "fullness" to your lead vocal(s). This actual term is mainly predominant to define the back-up and/or background vocals of Hip-Hop music. (Rap/R&B).
Even though you can find this "ad lib" track in many other genres of music, It's a regular practice for the basic construction of the aforementioned. Majority of the time, This track is recorded to add emphasis to specific lines and phrases, but WITHOUT actually saying that line or phrase SIMULTANEOUSLY; With these tracks mostly recorded without rehearsal and spur of the moment; Hence the derivative of the name "ad lib track".