A Brief History of Surround Sound
Multi-channel sound is not a new technology. The first demonstrations of multi-channel playback where as far back as 1938. When I find the patent number I'll put it up. It was a large resistor network (or as I remember). Later in the 60's various matrix encoding and decoding methods came about. Unfortunately, the results were less than satisfying from both a performance and marketing standpoint. The early systems were plagued by poor technical performance, software of highly variable quality and public indifference.
Surround sound is a speaker format with 2 or speakers usually placed to surround the listener. It was started back in the 1930’s with addition of two or three front speakers in movie theaters. In 1938 Disney created a new surround format for their film ‘Fantasia’. The speaker format that was very similar to the 5.1 surround format of today, with three front speaker and two surround speakers. A few years later 20 th Century Fox started using 3 front speakers and a single surround speaker much like Dolby Pro Logic.
In the early 70’s Quad became popular by encoding 4 channels of audio information in two channels. The delivery format was the LP record which could also be listened to in stereo. A special ‘decoder’ was required to actually hear the quad material. My first hearing quad was Quadrophenia by the Who which was available at the time. Currently this album is available in stereo only. The amount of separation between the speakers was somewhat limited as was the size of the sweet spot (best sounding location). There are a number of different methods for ‘encoding’ 4 channels in to 2 channels but it was CBS (SQ) and Sansui (QS) methods that were the most popular. Quad eventually failed because of the competing formats.
In the mid 1970’s Dolby Stereo came about which had its roots in Quad’s amplitude and phase encoding method. Dolby Stereo was used in the film (theaters) because it could be applied on the film at a much lower cost. There have been many films encoded in Dolby Stereo. In 1975 a new wider film format became available and with it the ability to have 6 discrete tracks (one for each speaker location) placed on the edge of the wider 70mm format. This also gave rise to the addition of a special subwoofer or Low Frequency Effect track. Close Encounters was the first film to use a subwoofer channel. This channel was called the ‘Baby Boom’ channel. Later the 70mm format was extended to have three front channels, two surround channels and a baby boom channel. This is the same format as found in 5.1 surround sound home theaters of today.
In 1982 Dolby Surround started showing up in home theater systems. It didn’t have center channel steering and other improvements found in Dolby Pro Logic, but was used on many videos just the same. It was the pre-cursor to Dolby Pro Logic.
In 1987 SMPTE (Society of Motion Picture and Television Engineers) developed a standard for placing six channels of digital audio on to a film. Around this time home theater was becoming very popular with Laserdisc and VHS video tape. Dolby Pro Logic was the system used for these mediums. It grew out of the original Dolby Surround which was the first version of surround sound for home theater again with its roots in (Dolby Stereo) but included a few additions like a band limited rear channel, channel steering mechanism, Dolby NR on the surround channel for greater clarity and less noise.
Dolby Pro Logic was what really put home theater on the map. It was a 4:2:4 system upon which the 4 original channels (Left, Center, Right, and Surround) were encoded to two channels (Lt and Rt). These two channels could be played back in stereo without losing too much of the audio information but it wasn’t without its problems. Because the process relies mainly on amplitude and phase changes it was prone to errors. When encoding 4 channels in to 2 channels any one of the four channels could adversely affect the other tracks. This mainly occurred with the center and surround’s but sometimes the left and right tracks could be affected. Sometimes the center channel could change the width of the stereo separation (left and right). The Pro Logic system also only allowed for a single channel to panned at a time. Sometimes the delivery method (VHS tape) could cause all types of problems it the playback head alignment was off. Dolby Pro Logic is still very much in used today but it is found only on consumer home theater receivers and is not the same thing as that found on film.
Next came discrete surround sound systems namely: Dolby SR-D, DTS (Digital Theater Systems), and SDDS (Sony Dynamic Digital Sound). At this time digital audio couldn’t actually fit on to the current analog audio area of the film. A number of methods were applied to get better sound, digital PCM. In the late 80’s digital sound was realized in movie theaters but it, digital audio data, wasn’t actually found on the film but rather a CD-ROM. The player would read the CD-ROM audio data, decode it and then send it out each discrete track. The film had a timecode track which a CD-ROM drive would read and synchronize to. This system used two tracks of linear PCM (Pulse Code Modulation) digital audio very similar to that found on CD-Audio discs. This had two problems at the time: 1) you could only get two tracks of PCM off a CD-ROM, and 2) The number of minutes on each disc was limited. To overcome this alternative systems where developed each with its own inherent strengths and weaknesses.
The two medium method of movie projection was also in question. It would be much more convenient to have both the image and sound information all on the film. Because of the bandwidth limitations of the film different compression methods where employed to reduce the audio bandwidth. The front runner was AC-3 which is a perceptual encoding method. It reduced the bandwidth to the point that the encoded 5.1 (6 channels) audio could be placed on the outer tracks (in-between the sprocket holes) of a Film. DTS also came out with their method and extended it to be used for digital audio on Red Book audio CDs.
In the mid 90’s the DVD was introduced. This allowed consumers the ability to watch movies with surround sound in their own homes. This included Dolby Pro Logic but also Dolby Digital 5.1 and DTS 5.1 encoding. The DVD (Digital Versatile Disc) can hold about 2 hours of video with audio. This is what really turned the Home Theater market around. Extensions to both Dolby and DTS systems added an extra center channel in the back. Dolby called theirs Dolby EX and DTS DTS-ES the EX and ES basically meant “Extended Surround”. The back channel (the 6 th speaker or center surround speaker) was actually matrixed together (amplitude and phase) with the Left and Right Surrounds so it can still be heard without any program material loss.
Two High-Definition audio formats then came in to focus: SACD and DVD-Audio. Both formats are for Audiophiles interested in un-compressed audio. Though both are high definition audio formats they differ so much that you need a player for each of them but currently many players play both formats. It also sparked another format war.
Currently HD-DVD and BluRay are the competing high definition video formats.