Dolby first came to prominence as a noise reduction process, invented by Thomas Dolby in the 1960s. Before his noise reduction process was developed static and hiss on magnetic tapes and optical film would spoil the sound of a movie. Various ways were tried to get around it, such as reducing treble but using this method could only go so far before the dialogue began to be distorted or muffled.
As tape was rapidly superseding optical sound reproduction (a process where the sound is recorded as a visible signal on the edge of the film and converted back into sound when the film is run through a projector which is fitted with the right audio capability) the Dolby Noise Reduction (NR) was applied to improving the sound on tape by electronically suppressing the noise which is inherent in magnetic tape recordings. Read more