“... developments start with the desire of the developer to get what he... wants so that he can use it."
Dr. Ray Dolby
For most of the second half of the twentieth century, magnetic tape was used in the making of most audio recordings, but there was always some background noise present on them. This tape hiss, or "white noise," was most noticeable in quieter musical passages.
In 1965 electrical engineer Dr. Ray Dolby (b. 1933) proposed the first magnetic tape noise reduction system. The task was to improve the signal-to-noise ratio of the recording, reducing the level of hiss without affecting the quality of the sound. His approach was to "compand" (compress, then expand) the sound. During recording, an encoding circuit was inserted between the recording source and the tape recorder; this compressed the dynamic range of the recording. During playback, a decoding circuit was inserted between the tape recorder and the playback amplifier, expanding the dynamic range once again. The quieter sounds in the spectrum received a greater proportional boost; the signal level dropped and was filtered in the higher frequencies (where the tape hiss existed). On playback the white noise was less audible.
Dolby's first system, Dolby A, was widely adopted within the professional recording market. When the lower-fidelity Philips cassette replaced the reel-to-reel machine, Dolby produced a simpler version and licensed it to cassette recorder manufacturers.
