Surround Sound Past, Present and Future

Surround Sound Past, Present and Future A history of multichannel audio from mag stripe to Dolby Digital Surround Sound Past, Present, and Future ilm sound, television audio, voices in religious epics, for example. and music playback formats Some formats switched this channel used to be distinctly different off by means of trigger tones when it products of industries often wasn’t needed because the track on workingFF in isolation. Recently, how- the film was particularly narrow, and ever, this has changed. The popularity thus very hissy. of surround sound in the home has Although film stereo lost favor in A history of brought these sound formats closer the 1960s and early 1970s due to together. And now new digital high costs of the magnetic formats multichannel audio multichannel technology is poised to and a slump in the film business, foster an even more consistent sound mixers continued to experi- from mag stripe approach to sound reproduction, ment with the effects channel. easing the burden on both consumer Formats such as six-track 70 mm to Dolby Digital and producer while providing high magnetic (see sidebar next page) fidelity not just to the tonality of live provided consistent signal-to-noise sound, but also to its spatiality. ratios on all channels, so mixers could use the effects channel to envelop the Origins of surround sound audience in continuous low-level ambient sounds. The effects channel The first commercially successful came to convey greater sonic realism multichannel formats were developed overall, not just the occasional in the early 1950s for the cinema. At dramatic effect. the time, stereophonic sound, a con- This expanded, more naturalistic cept new to the public, was heavily practice came to be known as sur- promoted along with new wide-screen round sound, and the effects channel formats by a film industry feeling as the surround channel. The extra threatened by the rapid growth of speakers at the rear—and now along television. Unlike the two-channel the sides of the theater as well to format later adopted for home stereo, create a more diffuse soundfield— film stereo sound started out with, came to be known within the industry and continues to use, a minimum of as “the surrounds.” four channels. With such film formats as four- Home stereo and “quad” track CinemaScope (35 mm) and six- track Todd-AO (70 mm), multiple Bell Laboratories’ famous early sound channels were recorded on experiments with stereo sound in the stripes of magnetic material applied to 1930s used three channels. Cinema each print. To play these prints, stereo in the 1950s was using no less projectors were fitted with playback than four channels, and as many as heads like those on a tape recorder, seven. Yet when stereo finally made it and cinemas equipped with additional into the home in 1958, only two amplifiers and speaker systems. channels were used. This was not From the outset, film stereo because of listener preference, or formats featured several channels some predisposition on the part of across the front, plus at least one audio professionals. Rather, two channel played over speakers towards channels (left and right) were all that the rear of the cinema. At first the the then-prevalent LP phonograph latter was known as the effects record could accommodate. channel, and was reserved for the Two-channel stereo music repro- occasional dramatic effect—ethereal duction was such a dramatic advance 1 By Joseph Hull Marketing Communications Manager Dolby Laboratories Inc. over mono—and so comparatively the time was broadcast TV, which easy to implement—that it soon provided distinctly low-quality mono 1,2 3 4 5,6 became the norm, even as filmmakers sound. For the next decade home continued to regard four channels as stereo, movie stereo, and TV sound the minimum necessary to create a would remain separate entities lifelike soundfield. A few years later supported by essentially isolated two-channel stereo FM broadcasting industries. A was introduced, further entrenching two channels in the consumer’s mind Dolby and film sound as “stereo.” Indeed, as time went on, only film buffs were aware that film In the mid-1970s, Dolby stereo, rare as it had become, contin- Laboratories introduced a new sound 1 2 3 4 5 ued to use more than two channels. technology for 35 mm prints origi- As home stereo grew in pop- nally called Dolby Stereo. Instead of B ularity, equipment manufacturers magnetic striping, it was based on began to look for ways to expand the photographic, or optical, sound- their market. This was one motivation track technology used to put mono Optional stereo surround behind the ill-fated four-channel, or sound on film since the 1930s. quadraphonic (“quad”), home format For compatible playback in 6 promoted in the early 1970s. It mono theaters, the new stereo required two more speakers in the soundtrack had to fit the same space 70 mm Magnetic: rear corners of the listening room to on the print occupied by the mono Forerunner of Today’s reproduce two extra channels from track. Experiments showed that two specially encoded program sources. tracks, treated with Dolby A-type Digital Sound Because the existing home stereo noise reduction, could give excellent n the 1950s, movie prints with media had only two channels and fidelity. But trying to squeeze in magnetic stripe soundtracks pro- could not easily accommodate more, more than two tracks raised noise to Ivided the first multichannel sound several schemes were developed to an unacceptable level, even with ever heard by the public. 70 mm prints (A), for example, featured six encode the basic two channels with noise reduction. tracks, originally configured as five additional sound information. Most Two channels, however, were identical channels across the front were based on matrixing techniques not enough for movie stereo. As well plus a surround channel to the sides which enabled “hiding” extra chan- as left and right channels, a separate and rear of the auditorium (B). nels within the two regular channels center channel and speaker are As screens became smaller, reducing the need for five screen by recording them with different necessary to localize dialogue for channels to carry dialogue, Dolby relative phase. viewers seated off-center. In addi- Laboratories proposed the configura- Quad failed to capture much of a tion, “stereo” and “surround” had tion shown above, which has been market. There were several incompat- become synonymous to most of the standard since the late 1970s: left, ible encoding/decoding systems, film industry, so a surround channel center, and right main screen channels (1,3,5), one surround channel (6), creating confusion. Producers and was also a must. Thus a way had to and two low-frequency-only “bass recording engineers couldn’t decide be found to encode just two physical extension” channels (2,4). on how to best utilize the extra tracks on movie prints with four Dolby also developed a technique channels. And most significant of all, channels of information—left, center, enabling 70 mm prints to carry two few consumers perceived any real right, and surround. surround channels, instead of the usual one, at the option of a film’s advantage from the format. The solution was found in the producers. This “stereo surround” 70 Quad was never associated with matrixing techniques first tried for mm format thus became the fore- the multichannel stereo formats used quad home stereo, but with the runner of today’s “5.1”-channel Dolby in movie theaters, and the term channels configured in the cinema Digital surround format with its three “surround sound” still wasn’t heard stereo norm—left, center, right, and front channels, two surround channels, and low-frequency effects outside the film industry. After all, the surround—plus some sophisticated channel (see page 5). only popular home visual medium at new “steering” techniques. 2 Left Subwoofer Center Right (Subwoofer optional) Power amplifiers 35 mm stereo optical print Dolby cinema processor Dolby stereo optical playback in the cinema. Surround Dolby stereo optical proved so sources (and the film industry with performance stereo music systems practical that today there are tens of still more program-producing oppor- were the norm. Audio as well as video thousands of theaters worldwide tunities). The laser disc, the highest- had expanded to include new program equipped with Dolby processors, and quality home video program source sources (audiocassettes, CDs). Car almost every major title is released in ever, was introduced. Television set stereo was coming of age, and the format. What’s more, the film manufacturers began to offer products personal headphone portables were industry experienced a kind of with what might be called high- providing a new way to listen to renaissance in the 1980s, helped by a fidelity picture quality, and consumers music. A generation had grown up new commitment to high-quality bought them. Thus “television” listening to rock music that was as presentations exemplified by the became “video,” and the home TV set dependent upon audio technology as adoption of Dolby Stereo. That became a “video monitor” to display a musicianship—the same generation rebirth was also helped by the wide variety of visual program that was now being regularly exposed “video revolution.” sources, much as stereo systems play to multichannel surround sound in music from a variety of sources. the cinema. Against this background, The video revolution Dolby Surround was introduced late Stereo comes to video in 1982 for playing videos of theatri- The first videocassette machines cal films originally produced with were introduced in the early 1970s, As the video revolution got Dolby encoded soundtracks. promoted initially as time shifting underway, consumers were not only The original four-channel Dolby devices to record TV broadcasts for accustomed to high-quality stereo encoding remains intact when such viewing at more convenient times.

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