Boy; does this thread bring back memories
Back in the early 70's to early 80's I used to buy special dBx encoded vinyl records. They were awesome; S/N ratio of 90 db or greater, tremendous bass, very clean highs, no pops, clicks, or rumble of any kind. As they were compressed 50 percent with dBx encoding, the groves were very close tighter & only one half of the vinyl was used so very long playing records could be made which was great for classical of long jazz pieces. They could get up to 50 minutes playing per side.
You did need a dBx decoder to play them otherwise they sounded awful as they were so compressed with the dBx encoding. You could use the decoding half of a dBx encoder/decoder to play any dBx source material.
The was also a company called Barclay-Crocker that made custom 7 1/2 inch open-reel prerecorded tapes for many years. All of their tapes were recorded 1 to 1 on professional machines & with Dolby B (10 db noise reduction - this was before Dolby C). They were very clean (for the time).
When Dolby C (20db noise reduction) came along the CD was also introduced at about the same time. Barclay-Crocker made the decision to skip Dolby C in favor of dBx as it had 50 percent cleaner sound then Dolby C (40db vs. 20db) & made the custom tapes sound as good as CD's.
I bought a lot of the dBx encoded tapes from them just before they went out of business. Yes, the CD killed them.
I also recall the fight over which noise reduction method was going to be used for the then new TV stereo sound transmissions. Fortunately for all of us, dBx won out as it was simply the best available. So, today all non-digital TV stereo sound is sent out dBx encoded & the TV set decodes it. As all TV's have a dBx decoder in them, I assume that even digital TV sound is dBx encoded before it is digitized & transmitted. I'm not sure about how Dolby 5.1 surround sound is handled but it too may be dBx encoded then decoded at the TV set before going through the Dolby decoding circuitry.
One thing is certain... we have come a long way in the last 30 years. Things that we could only dream about then are common place today.
Isn't technology wonderful.