The forums, the youtube videos, the emails, the questions.... We'd all like the processes of how music is made to be simpler to understand, but the reality is that audio engineering has a huge learning curve. In answering a question that came to me, I thought it could be interesting for our readers as well.
Today, I'll give some insight to mastering and remastering. In general, the mastering engineer is working with the final "mixes" provided by the producer or label. The mixes are usually in stereo and come from decisions made from the 'multitrack' record (see #133 Cookie's Corner).
A remastered version uses either the final mix/master copy to create a new production version of the song or album. "Remastering" can also mean a second production master that intentionally has a different sound from the original mastered release.
The primary job of a mastering engineer (and remastering engineer) is to create 'masters' suitable for making a product that:
A) is the master used for producing multiple copies for different formats like vinyl, CDs, SACDs, cassettes, etc.
B) is the master digital copy used for consumers to download or stream.
Generally, the producer, artist or label provides the mastering (or remastering) engineer the mixed (or previously mastered) tracks as the source. The mastering/remastering engineer generally creates the production copies in multiple formats for manufacturing or consumer download. A lacquer would be made for vinyl production. A DDP or PMCD would be made for CD replication. An interleaved audio file might be used for consumer digital download or streaming.
In the best possible cases, the mastering engineer does not alter the sound of the mix unless they need to conform to certain specifications for production or are paid by the producer/artist/label to make adjustments to the sound.
Example... when I worked for Windham Hill Records, I was a producer with a budget and timeline to meet. When we finished the mix, we didn't often have time to adjust the volumes between songs or adjust spacings for vinyl release. We'd ave that for mastering. Sometimes, a track needed eq or compression to meet the specifications of vinyl. I'd go to Bernie Grundman's and he ran it through his systems to create the production lacquer. CDs and cassettes have different specs so we'd master a different master for each of those.
Depending on the requirements of the label, it's possible that each format (vinyl, CD, mp3, SACD, DSD, 1/4" tape) will be slightly different in sound in order to conform to certain specifications. Not all mastering studios have the same gear. You could run the same changes elsewhere and have an entirely different sound for your master. That's the importance of the gear each mastering studio had.
Unless it is requested by the label, when we remaster an album for Blue Coast Music to DSD256, we try to do as little change to the mixed/mastered file provided. We created a proprietary process called SEA for this remastering to DSD that is analog. We try not to alter the mix but restore dynamics and widen the image when possible specifically for DSD256 release.
Audio engineer processes are not easy to understand and are not simple. I hope that my explanation helps a little bit. :)