In multi-track recording, those tracks that are recorded first. In general, the rhythm tracks (guitars, bass, drums, et al).
"I just received my CD in the mail today. I am very pleased with the results!!!! I want to thank you for the work that was done. You read my ideas on how I wanted the CD to sound........no noise.......cymbals clear........and the final product was as I expected. Thanks again Dr. Coban and staff! Cordially,"