THE HEART AND SOUL OF THE MASTERING SIGNAL CHAIN ARE THE LOUDSPEAKERS. More than any one device, these are the main link of the mastering engineer to both the reference point of the outside world and the possible deficiencies of the source material. More great pains go into the monitoring system than just about any other piece of gear in the studio.
Probably the one biggest and most important piece of equipment that a mastering engineer can have is his monitor, and he has to understand that monitor and really know when it’s where it should be. If you know the monitor and you’ve lived with it for a long time, then you’re probably going to be able to make good recordings.