Dude, analog tapes transferred to digital from that era are ridiculously noisy. There's hiss and hum and buzz and digital only exacerbates that noise. It's not that what was recorded was poor or bad or wrong, it's the tape medium that's at issue.
That's why nearly every record from the 60's, 70's and 80's has been meticulously re-mastered for the digital medium. For one, analog tape degrades with every single pass on the heads. For a digital transfer to occur, tapes have to be baked in an over at a certain temperature, even tapes that have been in humidity free vaults for decades, or the tape would shed and crumble.
Every mastering engineer, or in this case, Bruce Botnick, a famed recording engineer, takes great care in preserving the original sound. There are all kinds of De-Humming, De-Noising, De-Buzzing and similar noise reduction programs that can remove all of the noise without destroying the audio but even they need to be used carefully, as to not destroy the integrity of the original recording.
This process can take months, even years (look no further than the Beatles catalog remasters at Abbey Roads) but this art has been nearly perfected.
It's not called the National Academy of Recordings Arts and Sciences for nothing.
