Dolby WAS for LPs. The tapes on which the music was recorded, before being cut to LP, were done with Dolby A. The extra two processing steps could not help but to compromise SQ, but for the reduction in hiss. What rvpiano has described has been written of over a long number of years.
Dolby A is very complicated and works on the entire spectrum.
On the older recordings, whether in LP or CD form, you can hear the tape hiss. On the later ones you cannot. Of course, there are other post-production anti-hissing devices that may be in use to mitigate this.
Of course, as has been said, earlier recordings were made with much simpler techniques, to wit, fewer and very carefully placed microphones. That may also account for an airier presentation.