For those wondering what “optical sound” is: it’s a “means of storing sound recordings on transparent film” (https://en.wikipedia.org/wiki/Optical_sound), in this context likely as sound on film, “a class of sound film processes where the sound accompanying a picture is recorded on photographic film, usually, but not always, the same strip of film carrying the picture. Sound-on-film processes can either record an analog sound track or digital sound track, and may record the signal either optically or magnetically. Earlier technologies were sound-on-disc, meaning the film's soundtrack would be on a separate phonograph record.” (https://en.wikipedia.org/wiki/Sound-on-film)

he Gold and Red Libraries (Gold effects start with “G”, Red with “R”)) consist of high-quality, first generation copies of original nitrate optical sound effects from the 1930s & ’40s created for Hollywood studios. They were collected by a prominent sound editor who worked in the industry for 44 years. The fragile optical elements were donated to USC, and transferred to tape by USC Cinema students in the early 1970s.