I've been listening to these and the quality is amazing...
This is the revival of the Peabody Award Winning Radio Drama, (CBS Radio Mystery Theater) originally broadcast from 1974-1982, rebroadcast in 1998 and 2000.
Radio veteran Himan Brown returned to the studio in 1973 to work on an ambitious project to revive the "golden age of radio" in the form of audio drama. This project was known to most as the CBS Radio Mystery Theater, but it always referred to itself as Mystery Theater. It presented the opportunity for the writers and actors of the "golden age of radio" to reunite in the name of the theater of the mind. The show was quite successful, running for nine years with an impressive 1,399 total episodes.
The show was never syndicated, so any all episodes out there were once taped from the radio, many with mediocre to poor quality. The show's revival in 1998 and 2000 meant that Mystery Theater was on the air once again, but this time it could be recorded with better recording technology. 132 of the 137 known episodes in the revival are here, most are the highest quality in which this show can be heard.