Thank you for the tip Enrique
This might be in the master buss, the step just before the mastering tasks. In that part is also usual use hardware like eq´s/compressors/enhancers for apply in the general mix. Due to you are interested in it I´m going to include that part in the post too.may I suggest a highpass/lowpass in the beginning of the list and a master reverb somewhere (only applicable for mixes that are too dry which is very frequent nowadays)
It´s better the Trascending Music emulation of that hardware. Well, really it´s A LOT OF MORE better.also, if using the HO Apex Aural Xciter, it works best in parallel than in serial (too much of an effect in serial)
It´s very usual, the hardware most used for this is the Cranesong Heed 192.- thank you - really great the triodes/pentodes tip in serial.
This is based in the psychoacoustic theories where you work int the harmonic content of the audio for change the general perception of the sound.