Dolby Stereo

**Dolby Stereo** was the first ever theatrical audio format used by Dolby Laboratories, created in 1975 and first used on films the next year in 1976. While Dolby had appeared in some capacity in cinema as early as 1971 with the likes of *A Clockwork Orange*, they mainly pertained to just audio mixing and noise reduction services. However, wishing to solve limitations in the traditional Academy optical audio tracks, envisioned a system to push multi-channel audio to the masses (which had mostly been relegated to large cities due to reliability issues); and thus Dolby's long-standing reign in the theatrical arena had begun.

Technically, the brand name is used on two unrelated technologies for each type of film - **Dolby SVA** and **Dolby Stereo 70mm Six-Track**, for 35mm and 70mm prints, respectively.

## Dolby SVA

Co-developed with Kodak, optical soundtracks on a Dolby Stereo film carries not only the left and right tracks for the traditional stereo sound, but also (via an encoder known as the *Dolby Motion Picture Matrix*, or "MP" encoder) both a third center and a fourth surround channel for speakers on sides and rear of theaters to encode sound effects into extra channels. Making use of the former mono optical channel space in the Academy standard, four audio channels were generated, similar to a Quadrophonic design and enabling multi-channel audio on 35mm prints of films for the first time in a widespread capacity. Additionally, Dolby A noise reduction was applied to further clear up audio tracks in the process.

First making use of the Sansui QS matrix from 1975 to early 1979, it was later replaced by a custom enchanced matrix developed in-house by Dolby themselves. To permit for backwards compatibility with older systems, an optical soundtrack was also provided on the space, allowing for it to be used in mono and older stereo auditoriums.

An early version of the system made its debut without the surround audio channel with *Lisztomania* in October 1975, with its full debut with the surround audio channel first appearing on *A Star is Born* in December 1976.

Dolby SVA would be succeeded by **Dolby Stereo Digital**, better known as **Dolby Digital** in 1992, with a fallback analog Dolby SVA track included on 35mm prints of those types of films.

## Dolby Stereo 70mm Six-Track

Unlike Dolby SVA, this format proved to be far more simpler to develop. On Dolby Stereo Six-Track, all that differs from a standard 70mm print is that Dolby A noise reduction is employed on the six magnetic tracks as the audio arrangement was taken from the earlier Todd-AO format from 1955. Initially under the latter format, the audio layout was for five front channels and one surround channel; but as time passed the "middle" left and right audio channels had been neglected, with those channels either being completely ignored or just simply duplicated the mix in the respective front channels.

Dolby did not approve of this practice, and for Dolby Stereo Six-Track these two channels were instead used for low-frequency enhancement (or LFE channels). Luckily, these two channels would eventually return to their high-frequency intentions for the later Dolby Digital format, with Six-Track serving as a genesis for how 5.1 surround sound had started (although here the implementation was for mono surround effects, rather than stereo surround in the latter format).

This format made its debut on 70mm prints of *Logan's Run* in June 1976. Unlike Dolby SVA, no successor to Dolby Stereo 70mm Six-Track was ever developed by Dolby Laboratories as Dolby Digital was for 35mm prints only.

## Trivia

* Initial adoption of Dolby Stereo was slow, but began to rapidly accelerate with the success of *Star Wars* in May 1977; allowing even smaller theaters to feature surround or even simple stereo sound for the first time.
* Starting in 1986, Dolby's Spectral Recording noise-reduction technology was integrated into the format to enhance audio quality further on prints, replacing the original Dolby A noise-reduction method. These prints went by the name **Dolby Stereo SR**, and natively added the center and surround channels onto the optical format without the need to decode.
* Dolby Stereo was intended strictly for theatrical use. However, due to the rise in home video and home theatrical exhibitions of films in the late 1970s and early 1980s, Dolby needed a way to adapt Dolby Stereo for home usage. This ultimately manifested into **Dolby Surround** in 1982.
* By the time of Dolby Digital's introduction into theaters, over 3600 films had been released theatrically with Dolby Stereo soundtracks.
* Prints of films featuring exclusively Dolby Stereo would be continued to be released for quite a few years after Dolby Digital appeared (especially on trailers of films), but by the end of the 1990s most films were in Dolby Digital only (fortunately featuring Stereo SR backup tracks as mentioned earlier).