Friesiansam is perfectly correct. The only way to know if a system of new component is better or worse than what went before is to know what went before intimately.
That is why, at the most basic, recording studios run a test tone of just one frequency through the system to balance everything up.
In the words of Captain Beefheart on Trout Mask Replica "The following tone is a reference tone, recorded at our operating level... "
I have been fortunate enough to have been at the recording of an album, at the stereo mix-down, the mastering for vinyl, the re-mastering for CD and own 12" and CD versions. That is my reference.