Roger Ford: Is it true that originally, the mono and stereo mixes would have been done by different engineers?
Mark Wilder (mastering engineer for the Dylan Mono Box Set project): True, for the most part. Without having the studio logs in front of me I can’t say for sure, but standard practice during this period of time was that the producer sat in with the mixer of their choice, and they mixed the mono record. And then that three track, or four-track would go to a night engineer or an engineer who didn’t have that much to do the next day, and they’d be told “OK, you have a day, mix this album in stereo.” So you often have someone doing the stereo who wasn’t as involved in the process as those doing the mono. So that’s why you have these great differences in feel, in everything, in stereo.
Steve Berkowitz (reissue producer for the Dylan Mono Box Set project): When we did the SACD for “Blonde On Blonde” [...] Al Kooper and Robbie Robertson sat in my office and I said “So what do you think? Is it all right?” And they approved it, and then just by chance Bob Johnston was in the building, and I said, “Let me ask you this question: how come, in ‘Just Like a Woman,’ the acoustic guitar in the second verse is to the left of center?” And Johnston goes “Shit man, I don’t know. We mixed that mono probably for three or four days, then I said ‘Oh shit, man, we gotta do stereo.’ So me and a coupla guys put our hands on the board, we mixed that son of a bitch in about four hours! I musta just done it with the knob to the left of center, man, I don’t know why!” So my point is, it took a long time to do the mono, and then it was, “Oh, yeah, we gotta do stereo.”
http://www.rdf.pwp.blueyonder.co.uk/MonoReissues/MonoInterview_ISIS153.pdf