I haven' t read all of it which could be dangerous, but fro a first brief glance, this guy does appear to be talking sense.
I aggree with dunky boy totally, that the earlier recordings do seem to have more life and realism about them, and I think he is right to attribute the cause.
True in the early days, orchestras and groups were more recorded together, not exclusively, as les pauls multitracking techinques got popular.
But its true, listen to 60s music, it still sounds fresh even now.
And the stuff used was VERY archaic.
Recorded on reels of tape, lots of things afftected the sound...the tape has a hf rolloff, magnetic saturation of tape heads causes a slight distortion, 3rd harmonic,
to get effects, only a few techniques were used, and this is a lot were modern music differs.
Reverb was made by a plate or a spring, a physical item.
Delay was used by a tape machine played back, shadows style, phasing and flanging was 2 tapes run slightly out of phase, and pressing your finger on the flange of the tape reel to modulate the speed.
These old effects are revered by modern musos. Nowadays, its all done by dsp dig signal processing, a chip with a program simulating the effect. Uh-oh...shades of chord dac 64!! maybe that's why it sounds a little computer.

:duck:
Synthesisers are simply pitch generators osillators producing simple waveforms...square, triangle, and then knocking bits off with a nice analoge filter, typcial sounds include the 60s sci fi, dr who music, also there was the mellotron, fender rhodes ep, hammond organ.
Mikes were valved, guitar amps were simple fenders with that lovely tone, nowadays, guitars can be recorded on a digital box which models these earlier amps, but doesn't quite sound the same.
Nowadays, music is cheap shit, anyone can get a computer, and get a groove, a beat and mess around with it, and maybe even get a hit record. Its like fast food, really appetising and a quick fix, till you get the urge again. There is no expertise as such, no 'trade to learn, appreticeship', just find out how the software works.
Just listen to some records recorded in the 1960s, the recording is very good, amazing, considering 40 years ago.
Nowdays, its more polished, produced, shiny, to grab attention, it sounds hifi, its over produced, just listen to a big american record say shania twain for this.
As regards how it is done, film and music and other projects are converging in their methodology....they have all the people responsible for their particular specialism on hand, record a bit, change a bit, re-take, edit, cut out, go over until you put it together and find what you like, and gets approved.
And yes, studios do add a little 2nd harmonics and 3rd harmonics to get a more listenable sound, and are aware that digital recordings can be lifeless