Note: This information has been incorporated into this page which contains a more in-depth discussion.
I received an urgent phone call yesterday from a man who had digitized several reels of 2″ 24-track analog recordings that he wished to re-mix.
The tapes were originally recorded in about 1978-1979 and he said that he needed them to have Dolby C noise-reduction processing applied to the files.
I did a bit of research, as that did not sound correct from an historic point of view.
Here is an approximate chronology of the major noise-reduction systems and their dates of introduction: