Dolby Surround marked the first time that Dolby made its appearance in the home, being the first application of its matrixing technology in the early days of home video released in 1982. It extracts the data from a theatrical Dolby Stereo print and decodes the sound into four channels by way of the Dolby Motion Picture Matrix encoder (shortened to MP encoder), the same encoders used for Dolby Stereo. In these, the input audio is decoded to a left and right channel (which are unchanged from the original Stereo print), a center channel (a equal division of the left and right audio with a 3 dB reduction in audio levels), and a surround channel. The surround channel is similar to the center channel, but with a frequency band of 100 Hz to 7 KHz applied, a pass of a slightly modifed form of Dolby B noise reduction added, and a phase shift of 90 degrees to equal 180 degrees between the left and right channels.
After the initial input through the MP encoder, two outputs are generated: the left total (or Lt), and the right total (or Rt). These would be carefully mixed and balanced in each channel so that center audio do not go into the surround channel, which would a form of crosstalk to occur. The second stage of the Dolby Surround process involves the decoding of these outputs through a Dolby Surround decoder. Here, the Lt and Rt channels are inputted into the decoder. As Lt/Rt's cardinal directional channels are unchanged, they naturally decode into the left and right speakers, respectively; and since they also contain the center channel, that too is decoded as a sort of "phantom" image between the left and right speakers. For the surround channel, however; the decoder enters a L-R stage to extract the surround channel from Lt and Rt. To extract that channel, it first takes the difference between Lt and Rt, then goes through a short time delay line, and then goes through both a 7 KHz low-pass filter and a second pass of Dolby B noise reduction, before finally being outputted to the surround channels. To ensure no leakage of surround effects in front speakers, a very brief time delay is applied to ensure leaking sound effects come right after their front speaker counterparts.
While a bit limited for its day, Dolby Surround ensured a rapid advancement in the world of audio in the home video market in its relative infancy at that time. The technology would prove to be so popular, it was adapted for various other applications such as television broadcasts, and starting in 1990; video games.
Dolby Surround was extended by Dolby Pro Logic in 1987, itself succeeded by various extensions to the Pro Logic line; of which Dolby Surround would retroactively be classed as and would be backwards compatible with. The technology overall was eventually succeeded by Dolby Digital (more specifically the home version introduced in 1995), but the original Dolby Surround technology would survive well into the mid-2000s with gaming applications in mind. Finally, the Dolby Surround name would be re-used in 2014 for Atmos-compatible mixers to decode non-Atmos content.
Trivia[]
- Dolby Surround audio tracks first appeared on Betamax and VHS tapes as early as 1982, and by the end of the decade the overwhelming majority of major studio releases contained such a track. This would continue until both formats' ends in the mid-1990s and the mid-2000s, respectively.
- Television shows would make use of Dolby Surround soundtracks for broadcasts starting in the early 1990s. This would be a real-time effort unless such broadcasts were time-shifted and recorded. Many shows would make use of Dolby Surround soundtracks, but would gradually be replaced by Dolby Digital soundtracks starting in the early 2000s. However, some shows continued to make use of Dolby Surround for maximum compatibility with older sets and equipment until the early 2010s.
- As for games, the Dolby Surround technology would prove tricky to implement for real-time, non-linear sound effects at first (and given the limited sound capabilities of early platforms, it isn't hard to understand why). However, it would eventually begin to appear in games as early as 1990, starting with the PC Engine CD/TurboGrafix 16 port of Darius in March 1990. However, it would be another year before the next game with Dolby Surround would be released, the Super Famicom release of Final Fantasy IV in July 1991, with its North American Super Nintendo counterpart that November retaining the support of Dolby Surround. However, this game did not feature full licensing from Dolby Laboratories; the first Dolby-licensed game on SNES would be King Arthur's World in November 1992 a year later. From there, a small smattering of some cartridge-based games throughout the SNES and the Nintendo 64 would make use of Dolby Surround (some featuring the official Dolby license, and others unofficially), but it would become much more popular on CD-based platforms like the Sony PlayStation along with the PlayStation 2, the GameCube, and various Windows platforms and games. While it was gradually replaced by Dolby Pro Logic II starting on sixth-generation hardware (especially since it had a dedicated gaming mode) and sometimes Dolby Digital, some games continued to make use of standard Dolby Surround sound options until 2007. In fact, special trailers were made specifically for Dolby Surround's usage for gaming in the early 2000s.
- Dolby Surround would also appear on LaserDiscs and also serve as the minimum supported audio format for the DVD format, sometimes to preserve original theatrical Dolby Stereo audio mixes on the format. During the format's earlier years, Dolby Surround was employed as either a secondary or the main audio track for the vast majority of releases, though this would gradually be superseded by Dolby Digital as well.