It is time to say goodbye and a big thanks to Ray Dolby, and Dolby Laboratories for making my earlier years sound so much better.
Ray Dolby died on September 12, 2013.
With digital recording you convert the analog audio stream into binary 1's and 0's meaning that copies can be made without degradation.
But in earlier years tapes recorded analog audio directly to tape. And this included a lot of /hiss/ . Sometime when copies but also when recording music with a large dynamic range, you needed to set the recording level low to cope with the loudest signals, but then the low level passages became hissy.
Dolby Laboratories came up with essentially a filter that changed what was recorded to analog tape, and on playback reversed that change.
Quieter and High Frequency signals get boosted maximally on record, and reversed on playback
The two popular technologies that Cassette players utilised were Dolby B and C. Dolby C gave better hiss reduction, however if you played back your Dolby C tape on a player without Dolby if sounded pretty abnormal. So many people chose to record with Dolby B so they could do playback on their Car stereo's or Walkmans which typically did not have Dolby.
Dolby was normally integrated into your Hi-Fi cassette deck recorder though you could buy a standalone unit and pass your signal e.g. radio/ live audio source through that unit on record, and back out on playback.
Dolby was licensed so manufacturers had to pay Dolby Labs for use of their technology, units with inbuilt Dolby were therefore more expensive.
Equipped with Dolby B you could get a 10 Decibel Noise (Hiss) reduction. That was pretty dramatic.
And so my many analog recordings of 20 years ago always benefited from Ray's technology, making them [almost] hiss free.
Thank you Ray.
Making Cassettes Sound better
Dolby Noise Reduction
Dolby at Engadget