With respect, there appears to be a number of differing processes conflated within the context of this thread.
Perhaps its sign of progressive, well-developed ongoing conversation. Something society in general would greatly benefit from.
The real point about the majority of re-masters, the reason they were introduced in the first place, is because of ongoing technological development in users listening habits.
When recordings were first mastered, although their level was maximised at that stage (mastering is the stage between the recording studio and record plants mass duplication), it was commonplace for there still to be a good amount of headroom in the master.
Further maximisation could result in needles on playback arms skipping. So, the playback medium dictated a need for headroom that allowed natural dynamics to be present. That resulted in excellent recordings that fell on the ear in an entirely natural manner, as dynamics are a natural element of musical sound waves.
Consumers would put an album on the turntable and utilise the volume control on their audio system, to control the level of playback to their taste.
On many of today’s audio playback devices, digital tracks are a highly customised mix. The singular preferences of one individual, often shuffled on a revolving carousel. Not the choice of an artist or producer.
Therefore, different artists, different studios, different mastering engineers, different musical genres, side by side, back to back. Often their levels are normalised to make them more even in volume level from track to track.
To the average human ear, louder sounds better. Thus, in the highly competitive recording field, a record company, knowing its recordings will often sit alongside other company’s recordings and be directly comparable. Remaster their back catalogues of older recordings to ensure their levels remain fashionably competitive and don’t sound wimpy by comparison.
There are other reasons why some recordings are re-mastered, one is because when digital recordings first appeared, it was a novel, immature technology, in the same way that the earliest analogue recordings once were, with their wax cylinders, trumpet horn speakers and needles one could use only once.
Therefore, as digital recording technologies matured, some artists elected to re-record and re-master their catalogue for posterity. As artists always want to sound their best, and also because they want their recordings to sound good competitively, as previously explained.
Kate Bush’s re-recorded (to analogue tape) and re-mastered back catalogue would be one example.
Re-recording can present many, many challenges and certainly did so for Kate. Keys were changed in certain instances.
However, re-mastering can also present challenges of its own. For instance, one day I had a phone call from a mastering engineer in New York.
He had been given the job of re-mastering the entire catalogue for “The Rolling Stone’s Anthology”. Unfortunately for him, certain of their early recordings had been taped, on a three-track machine.
Many of you will be unfamiliar with that format, so I should explain that early two track stereo recordings were extremely ping pong, to coin a phrase. The sound was good to the left or right, but these recordings, lacked a strong central image.
Ultimately, this problem was overcome with advancing electronic design incorporated into Large Format Recording Consoles, and pan controls appeared. But in the interim, three track machines were developed, so there could be a left and right track, with the third track greatly strengthening the central image.
The problem is today, three track machine are extremely rare indeed. Even if one could locate such a machine, the chances that it would be fully serviced, in good working order, able to be utilised to playback the original master tapes is highly doubtful. The rubber wheels wear which the tapes pass through and disintegrate over time etc.et al.
The Mastering Engineer was given to understand, I could be likely to possess such a machine, thus I was contacted by him.
The salient point is, technologies change.
All too often record companies and recording studios alike sell or throw away their outgoing technologies, dispensing with them completely.
A small number, keep everything and maintain everything, but that presents ongoing costs and valuable storage space; so very few, usually, only the very best of the best, are thus inclined and can afford to.
In addition, record companies tend to see their huge back catalogues as a wonderful cash cow. No artist to pay or composers royalties, its money for old rope. Re-mastering? Engineers have regularly suffered from ridiculously low budgets, so have developed cost effective methods to approach these tasks, to remain commercially viable.
Thus, the traditional time and effort that would go in mastering, tends to be reserved for the most commercially successful artists. Or those with a following that possess remarkably acute, aural sensibilities. Along with the ludicrously high-priced, designer playback systems, necessary to deliver the sonic delights, they are normally accustomed to.
Others may have re-masters derived from all sorts of less than ideal sources, dependant upon the unrealistically low budget the Engineer was presented with.
Various hardware and software solutions exist today, that facilitate the effective cleaning up of the disadvantages, such deplorable situations always will present.
But it explains why there is a great disparity in the quality of various re-masters, some being great, others appallingly bad, and many of course, lying somewhere in-between.
Finally, when 5.1 technologies were first introduced, a much admired, dear colleague, sadly no longer with us, had the foresight just in case the system became popular and for posterities sake; to create 5.1 mixes of whatever recording he had just mixed for stereo reproduction.
Few had his foresight, or indeed his great talent, and thus as with previous bouts of re-mastering, less than ideal, but efficiently workable methods of re-mastering for a new format, can come into play. Dolby ATMOS will involve further re-mastering of back catalogues in a similar fashion.