Adjusting the relative levels of instruments or recorded tracks.
"Dear Dr. Coban: Just got back to Rhode Island. Thanks to you and your staff the long 23 hour drive seemed shorter because I was able to spend some of those hours listening to "The Hi-Fi Nightingale." You did a terrific job restoring the voice and orchestration of this badly worn and abused 45 year old monophonic LP. I can now look forward to ..."