In the 70’s I made some recordings of my Jump Blues/Swing band playing live, using a pair of omni condenser mics straight into a Revox A-77. No pre-amp, no mixer, no EQ, no compression, no limiting, no noise reduction---no nuthin’. Those recordings sound more like life music than 99.99% of my LP’s and CD’s. I use them to evaluate Hi-Fi equipment, especially loudspeakers. I also recorded solo speaking and singing voices, and those recordings are invaluable for ascertaining the freedom from vowel colorations of speakers. Electrostatics = excellent; magnetic-planars = very good to excellent; dynamics (cones and domes) = okay to very good; horns = not so good. Just kidding!
The sound on 50’s and 60’s LP’s are recording engineers of the time attempting to make "High Fidelity" recordings, capturing the sound of live music. The closer the sound of the recording to live sound, the higher the fidelity, of course. In the documentary I mention above, Tom Dowd is shown in the studio, walking around the musicians, stopping in front of each and listening. He then returns to the control booth, making adjustments to his recording equipment to make the sound in his monitors more closely resemble that of the live sound he just heard in the studio.
When I’m in the studio now, the engineer usually compares his recorded sound, not to the live sound in the adjoining room, but to commercial recordings, a/b’ing between his recording and a hit CD. It’s relative fidelity, not High Fidelity. The intent of engineers now is quite different than that of the guys who made the recordings "we" think sound so good. "Fidelity" is now a quaint notion, of relevance only to audiophiles. Hardly the target audience of the vast majority of record companies!
But the best recording engineers of today (Kavi Alexander of Water Lily, Keith Johnson of Reference Recordings, Pierre Sprey of Mapleshade, Barry Diament of Soundkeeper Recordings) are as good as any of the old-timers, maybe better!