I have a conundrum that I hope someone will have an explanation for. Let's start with talking about CDs. One of the best quality CDs that I have is a double live recording of the Cowboy Junkies. It was recorded in the 90s. I still have a late 90s Theta Miles CD player (Theta also made hugely expensive Transport / DAC separates) - I use the Theta transport with a MHDT Havana ladder DAC in my garage / garden system. As an integrated CD player the Theta Miles was a big improvement on my prior Marantz CD63SE but compared to my subsequent Oppo 95 and now (I use the Oppo as a transport) Topping D90SE DAC, the Theta sounds truly dreadful. That is bloody awful. Now I guess we have all been prey to buying the latest and best-est, and only years afterwards subject to sellers remorse. The change from valve to solid state (I had triode Leak KT66s and went to a Dynaco ST400 and of course changed speakers) which although a marvel at the time was again in comparison bloody awful. The change from analog to digital led to much the same kind of experience of remorse, if only in retrospect. Enter again the Cowboys Junkies live CD and their equally well recorded Trinity Sessions - there is a later re-recording of the original and both sound find. Both were obviously recorded on tape (you can hear the hiss) and then processed digitally. I have also recently been playing some 1950s blues and early rock which apart from the absence of bass and upper treble (probably due to the microphones on the time) and general thinness of tone are very listenable - by this I mean that the tones of voices and individual instruments are recognizable and real. Most of these blues and rock recordings were 'digitalized' to CD in the late 1980s and 90s. So here is the conundrum. Why is it that 1990s digital recordings using an ADC (analog to digital converter) sounds pretty good or at least listenable okay by today's standards (using a modern DAC), whereas the reverse process using say a 1990s DAC sounds crap. I accept that recording studios could afford the best technology for the time (unlike me) but in fact even the best technology at that time is pretty poor by today's standards. So why do late 1980s and 90s ADCs not make a mess of the music whilst the opposite using DAC conversions do make a mess of it. Answers please.

Trinity Sessions was recorded onto digital tape - R DAT - with a single Calrec Ambisonic mike.
There should be no hiss ?
I only have Trinity Sessions on LP, just gave it a spin, no hiss.
Had it on German CD, long gone.

Analogue recording may be the key to those early CDs sounding good.
Often unmolested transfers remastered to digital without the meddling that is endemic today.

Remember the warning some early CDs carried ?

Some guff about digital being so good it would expose defects in the original recording, the reverse was the reality.

Maybe the answer is that 1980s ADC's (in particular - think : great Philips and Decca recordings B-} ) and DAC's were both multi-bit. Whereas by the mid-90s both ADC's and DAC's were single-bit.?

positive-feedback.com/Issue65/dac.htm

Also a lot of the early CD's were straight transfers to digital with no fiddling to "improve" things