Noise Reduction

Although many seasoned R-R enthusiasts are not overly troubled by background hiss, there have been many different  approaches to improve signal-to-noise ratios over the years.
The most prevalent of course is Dolby but back in the 70s, DBX was gaining market share.
Dolby, available to Studios & Consumers reached a great level of refinement in the 90s with Dolby S.
Other interesting offerings emerged targeting the studios and recording engineers.