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Surrounding sound
An introduction to the world of home theatre
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by: Carol Mazur
Dolby Surround sound was the first multiple channel audio system that gave us cinema sound at home. In basic form, besides the normal stereo channels, surround sound adds a centre speaker at the front to enhance the clarity of dialogue and rear speakers to add depth for ambience and special effects.
 The four sound channels are encoded into the film and a decoder is used at home to recover the information. Hang on … four channels but five speakers? Yep, that's because in basic Dolby the surround sound sent to the rear speakers is actually mono, or single channel, sent to two speakers.
Surround innovation has gone way past basic Pro Logic with the introduction of Dolby Digital (AC-3), Lucasfilm THX and DTS Surround. However, the thousands of video movies on the market that still feature Dolby Pro Logic as their surround sound system means it's still a major part of our lives and will be for years to come.
You can watch Dolby encoded films with a normal stereo set-up and still hear the entire soundtrack, but you lose the special and spatial effects. If you want to appreciate these fully you need to look at a product that uses Dolby Pro (Logic or other) processing.
These units are intricate devices but incorporate a noise sequencer that allows easy balancing of the levels from all four channels so that fine-tuning the system is a straightforward operation. So here's how it all started.
The first film shown publicly with stereo sound was Walt Disney's 1941 release of Fantasia. Three optical sound tracks and a control track on a separate 35mm film were played in synch with the picture.
The first commercially successful multi-channel sound formats were developed in the early 1950s. Unlike stereo for music reproductions however, stereo cinema films used a minimum of four channels. One channel, at least, was directed to the back of the cinema for occasional dramatic effects.
Stereo films fell out of favour in the 1960s and early 1970s due to high costs and a slump in the film industry, but sound engineers continued to experiment with what had become known as the 'effects' channel. Side and rear speakers provided a 'surround' sound that enveloped the viewers in ambient sound and provided greater drama for occasional effects.
In the audio world, two-channel reproduction became the norm through the advent of the stereo LP and FM broadcasting. Attempts to improve on stereo, like the quadraphonic four-channel system, flopped. With two-channel music systems, monaural television, and surround sound cinemas, the three disciplines remained firmly divided for many years.
Changes began in the mid-1970s, when Dolby Laboratories introduced a new sound technology for 35mm film called Dolby Stereo. Instead of the magnetic striping of the existing film stereo formats it was based on the optical sound track that had been used to put mono sound onto films since the 1920s.
To allow playback in mono-equipped theatres the sound track had to be squeezed into the space occupied by regular mono sound tracks. Two channels treated with Dolby A noise reduction permitted this, but trying to fit in more channels raised noise to an unacceptable level. And due to the size of cinema screens, two-channel sound proved insufficient.
A separate centre channel was needed to localise dialogue for viewers who sat off-center. The film industry also had come to accept stereo and surround sound as the same thing. So to ensure mono-compatibility a solution was required that would it two physical tracks carrying four channels of information onto films.
The method developed has its roots in the matrix techniques first used in quadraphonic stereo. However, the playback channels are configured in the film stereo norm ( left, centre, right and surround. The technology was extremely successful. Home video recorders were first promoted as simple time-shifting devices and a new industry arose in their wake: cinema films transferred onto videotape for home viewing. Television manufacturers began to offer hi-fi TVs in response and 'TV' became 'Video' for most people.
Discerning viewers who were accustomed to high quality sound from their stereo systems and in the cinema searched out the improved 'hi- fi' video cassette players that were coming onto the market. The home theatre ball had started rolling. In 1982 Dolby Surround was introduced to the video world.
Original Dolby Stereo four-channel soundtracks were transferred intact to video cassettes or when broadcast on stereo TV and Dolby Surround processors made it possible to decode the surround channel at home. Dolby Pro Logic then made it possible to decode the centre channel as well and to take advantage of the sophisticated steering circuitry developed for cinema playback.
Practically every household already has an A/V system. Modern television and video programs are useless without a sound track and every TV with an internal speaker, however bad sonically, is an A/V system in its own right. There are sonic improvements to be gained by putting decent TV sound through a proper hi-fi system.
It's not just music programs that benefit. Sports, films, dramas and natural history programs suddenly become totally involving, giving you a genuine sense of 'being there'. With an audiophile quality hi-fi system the effect can be breathtaking.
So the real question is how many TV/VCR users can be persuaded to have real hi-fi sound accompanying the pictures? The news is good here and is actually not at all difficult to do. All you need (in the beginning at least) is a proper hi-fi amplifier and a pair of good loudspeakers.
Hook up the TV and VCR sound to these and you are away. This simple approach is logical for two basic reasons. One is that most people already have their main TV/VCR and hi-fi system in the same room. Both systems are rarely, if ever used at the same time; therefore once the prejudice of moving around the furniture is overcome, it makes total sense to put the TV screen midway between the speakers.
You then need only one set of seating positions, whether you are listening to music from a CD, to 'Life on Earth' on free-to-air TV or to 'Terminator Two' on video. The sound quality of most video software is now really good. Hi-fi VCRs and DVD players can offer sound quality that, at its best, is the same as compact disc (some would say the potential is there for it to be better).
Indeed, major film companies have invested heavily to ensure you can enjoy superb quality sound in your own home, whenever you want, and for the most part they have succeeded. Dolby Surround is not necessary for a basic home theatre system, but it's a great bonus, especially with modern movies. The extra hardware (a decoder, two extra amplifiers, speakers, etc), can be added to a proper basic system later as an upgrade.
In fact, some people argue that your existing stereo hi-fi and A/V system should be upgraded to your total satisfaction before you begin adding surround equipment.
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