Manufacturer's Report - Dolby Surround Sound Update #1 - January, 1995

By William Barnes


On behalf of Dolby Laboratories, I'd like to say hello and welcome to the premiere 1995 electronic issue of Secrets of Home Theater and High Fidelity! We are glad to be a part of this new venture, and we look forward to exploring the exciting world of home theater in the months ahead. In the coming issues we plan to discuss the current state of home theater, cover a bit of the history behind it, and also look ahead to see what the future holds. We're sure you'll find it both interesting and educational.

In this issue we'd like to take a look at the origins of home theater, where the market is today, and also take a peek at what the future will have in store.

Everyone Is Talking About Home Theater!
You can't discuss the concept of home theater without mentioning Dolby Surround. Dolby Surround is at the heart of the home theater movement, and it is this technology which makes it possible to experience multichannel audio in the home using today's delivery media. People are quickly catching on to this new experience, and the home theater market is one of the fastest growing areas of the consumer audio/video (A/V) market. Today there are over 14 million Dolby Surround systems in homes worldwide, with over 4,000 Dolby Surround movies available via broadcast and home video. In addition to movies, there are over 100 surround CD albums, approximately 50 television shows and even a few video games, with new titles becoming available all the time. Dolby Surround decoders are available in many product types and configurations, such as preamplifiers, A/V amplifiers, rack music systems, compact music centers, satellite receivers, and television sets. This wide variety of software and hardware ensures that there is something for everyone, and for every budget. But where did the concept of home theater come from? Perhaps we should step back and look at its' origin.

A Bit of History
In the world that we live in, natural sound has always been multichannel. That is, sounds come from in front of you, from the sides, and from behind you. Unfortunately, the first systems for recording and playing back sound were limited to just one channel (monophonic) due to their physical characteristics and the technology of the day. A monophonic system is certainly better than no audio at all, but it cannot do a convincing job of recreating the sorts of natural soundfields that we experience in real life. Creating a convincing, involving experience has always been the goal of movie producers, and so theater sound became one of the first commercial applications of multichannel audio in the early 1950s with formats such as four channel CinemaScope (35mm) and six channel Todd-AO (70 mm). These systems used stripes of magnetic material which were applied to each release print to record multiple channels of audio. Theaters could equip their projectors with appropriate playback heads and add the required amplifiers and speakers to produce a multichannel sound presentation.

The cost of adding magnetic stripes to film was relatively expensive, however, when compared to the cost of standard optical soundtracks, and this limited their use. So, in the 1970s Dolby Laboratories began working on a system which would allow films to carry multichannel audio on the optical tracks. This led to the development of a matrix system which used phase and amplitude changes to encode four channels of audio into a two channel soundtrack. Once the four audio channels had been encoded into two, the two channel soundtrack could be printed as two optical tracks on the film. The two optical tracks were placed in the location of the previously mono optical track so that prints using the system could be played in theaters with either mono or stereo playback systems. The optical soundtracks had a somewhat limited dynamic range, which translates into a relatively high noise level, so Dolby A-type noise reduction was added to provide better fidelity. The resulting film sound format, called Dolby Stereo, was introduced in 1976. Because the system was designed for use in theaters, where all attention would be focused on the screen and dialog would be an important part of the storytelling experience, it was decided to use three channels in the front (left, center, and right, abbreviated as L, C and R) and one effects channel in the rear (this came to be known as the surround channel, abbreviated as S). The left and right channels provided a normal stereo soundfield, while the center channel served to keep the actor's dialog anchored to the screen for viewers seated to the sides of the theater. The surround channel provided sound which would "surround" the viewer to help recreate natural soundfields and was mainly used for effects such as wind, rain and other low level "atmospheric" effects. Dolby Stereo allowed a single film format to provide mono, stereo, and four channel audio without the added expense of magnetic tracks. Any theater with stereo playback capability could add a Dolby Stereo decoder and extract the original four audio channels.

The Dolby Stereo format became very successful, with the result that thousands of movies were released with Dolby Stereo soundtracks. As the VHS/Beta war subsided and home video gained popularity, these movies were released on VHS video tape and laser disc, and the four channel matrix encoding went right along for the ride. As more and more of these movies were transferred to video and consumer interest in high quality home video grew, Dolby Laboratories began to think about licensing manufacturers to build matrix decoders which could be used at home to decode these video soundtracks.* Because the complicated active matrix decoders used in theaters were too expensive for the consumer market, a simplified version of the decoder that only extracted the rear channel was developed. This passive decoder, called a Dolby Surround decoder, was introduced in 1982. (The consumer system was called Dolby Surround to differentiate it from the Dolby Stereo theater system because Dolby Stereo involves the use of A-type noise reduction, while Dolby Surround does not.) As time passed, the system began to gain in popularity, and thanks to advances in integrated circuit technology it became possible to incorporate the same active matrix decoding as found in a Dolby Stereo theater into a single IC. This advancement made it possible to offer the system to the consumer marketplace, and in 1987 the active decoding system, called Dolby Surround Pro Logic, was introduced.

Back to the Present
Today, it's getting hard to find an A/V amplifier without Dolby Surround. Pro Logic decoders can be found in many different products ranging in price from $200 for a basic unit to $20,000 or more for a no compromises audiophile system. If you already have a TV, VCR, and stereo system, you can add a Pro Logic decoder plus center and surround speakers for as little as $400. So, owning a "home theater" doesn't have to mean taking out a second mortgage. Your local stereo store should be able to help you pick out the components that will work best with your existing equipment, or help you to design your dream system.

One of the reasons that surround is catching on so quickly is because the enhanced soundfield that it produces is easy to recognize. Unlike products such as audiophile amplifiers or expensive speaker cables, you don't have to be a critical listener with golden ears to appreciate the difference between an ordinary stereo presentation and a surround presentation. When the average person hears a Dolby Surround demonstration for the first time, there is an immediate recognition that there is something different, that the experience is more convincing, more life-like, more exciting, and enjoyable. This is one of the main reasons why Dolby Surround has been gaining in popularity so rapidly: the average person can easily perceive that it creates a new and desirable experience.

Now that surround has become popular, you may notice that there are stereo systems and televisions which have various surround sound modes that are not Dolby Surround. Well, not all surround sound is equal, and it is important to note that Dolby Surround is not just an add-on effect designed to simply produce additional sound from the rear of the room. It is a complimentary encode/decode system designed to deliver four channels of audio in a controlled manner. If your Pro Logic surround system is correctly installed and aligned, what you hear at home will be the same as what the producer heard in the studio when the soundtrack was mixed. This differentiates Dolby Surround from the other surround systems that some manufacturers include in their lower cost products, as these systems create an artificial surround effect as opposed to recreating what the producer intended.

Although it seems that the home theater industry is primarily focused on movies, there has also been a steady increase in the number of surround encoded TV shows. In addition to regular series such as Star Trek: The Next Generation, Deep Space Nine, Beverly Hills 90210, Melrose Place, The Simpsons, and others, all 102 games of 1994-1995 NFL Football season were broadcast in surround on the Fox network. This means of course that you can use your surround system frequently for regular television viewing. Unfortunately, not all surround TV shows display the Dolby Surround logo at the beginning of the show, although many do. On the CBS network, surround shows are indicated by a "Stereo Surround" indicator at the beginning of the show, and you may also see the Dolby Surround logo in the end credits of certain shows. To help you identify which shows are produced in Dolby Surround, we have included the following two lists of current and past surround shows.

William Barnes
Dolby Laboratories
San Francisco, California

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