Audio Quality - Network VTRs - 1970s

[kfbkfb]

On late night TV (USA) there are usually several
infomercials (Time/LIFE typically) advertising
compilations of, for example, Soul Music that was
featured on The Midnight Special (NBC 1972-81).

The sound quality is fairly good, I know that audio
can be enhanced, but, AFAIK, audio quality was
not a priority on (Network) "QUAD" VTRs.

I'm wondering why the audio sounds so good from
these old "QUAD" VTR tapes?


Kirk Bayne