The application of some form of signal processing before recording, that will be removed via complementary processing (decoding) during playback.
"I wanted to send this to thank you for the great job you did on our wedding music cd's- the quality is exceptional, they arrived back in short time and great shape. I've already told my friends about your great service! It's nice to know there is a place to send music to be restored and captured for posterity! Thanks!..."
