History of Multichannel Audio from Mag Stripe to Dolby Digital 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, reserved for the occasional dramatic and music playback formats effect—ethereal voices in religious used to be distinctly different epics, for example. Some formats F products of industries often switched this channel off by means workingF in isolation. In recent years, of trigger tones when it wasn’t however, this has changed. The needed because the track on the popularity of surround sound in the film was particularly narrow, and thus home has brought these industries very hissy. A history of and their sound formats closer Although film stereo lost favor in together. And now digital multichan- the 1960s and early 1970s due to high multichannel audio nel technology is fostering an even costs of the magnetic formats and a from mag stripe more consistent approach to sound slump in the film business, sound reproduction, easing the burden on mixers continued to experiment with to Dolby Digital both consumer and producer while the effects channel. Formats such as providing unparalleled fidelity not just six-track 70 mm magnetic (see to the tonality of live sound, but also sidebar) provided consistent signal-to- to its spatiality. noise ratios on all channels, so mixers could use the effects channel to Origins of surround sound envelop the audience in continuous low-level ambient sounds. The effects The first commercially successful channel came to convey greater sonic multichannel sound formats were realism overall, not just the occasional developed in the early 1950s for the dramatic effect. cinema. At the time, stereophonic This expanded, more naturalistic sound, a concept new to the public, application came to be known as was heavily promoted along with new surround sound, and the effects wide-screen formats by a film industry channel as the surround channel. The feeling threatened by the rapid extra speakers at the rear—and now growth of television. Unlike the two- along the sides of the cinema as well channel format later adopted for to create a more diffuse soundfield— home stereo, film stereo sound started came to be known within the industry out with, and continues to use, a as “the surrounds.” minimum of four channels. With such film formats as four- Home stereo and track CinemaScope (35 mm) and quadraphonic sound six-track Todd-AO (70 mm), multi- ple sound channels were recorded Bell Laboratories’ famous experi- on stripes of magnetic material ments with stereo sound in the 1930s applied to each release print. To play used three channels. Cinema stereo in these prints, projectors were fitted the 1950s was using no less than four with playback heads like those on a channels, and as many as seven. Yet tape recorder, and cinemas were when stereo finally made it into the equipped with additional amplifiers home in 1958, only two channels were and speaker systems. used. This was not because of listener From the outset, film stereo preference, or some predisposition on featured several channels across the part of audio professionals. Rather, the front, plus at least one channel two channels (left and right) were all played over speakers towards the rear that the then-prevalent LP phono- of the cinema. At first the latter was graph record could accommodate. known as the effects channel, and was 1 By Joseph Hull Marketing Communications Manager Dolby Laboratories Inc. Two-channel stereo music in cinemas, and the term “surround 1,2 3 4 5,6 reproduction was a dramatic advance sound” still wasn’t heard outside over mono and comparatively easy to the film industry. After all, the only implement, so it soon became the popular home visual medium at norm, even as filmmakers continued the time was broadcast TV, which to regard four channels as the mini- provided distinctly low-quality A mum necessary to create a lifelike mono sound. For the next decade soundfield. A few years later two- home stereo, cinema stereo, and channel stereo FM broadcasting was TV sound would remain separate introduced, further entrenching two- entities supported by essentially channel sound in the consumer’s isolated industries. mind as “stereo.” Indeed, as time 1 2 3 4 5 went on, only dedicated film buffs Dolby and film sound B were aware that film stereo, rare as it had become, continued to use more In the mid-1970s, Dolby Labora- than two channels. tories introduced a new sound As home stereo grew in popular- technology for 35 mm prints origi- Optional stereo surround ity, equipment manufacturers began nally called Dolby Stereo. Instead of to look for ways to expand their being based on magnetic striping, it 6 market. This was one motivation used the photographic, or optical, behind the ill-fated four-channel, or soundtrack technology used to put 70 mm magnetic: quadraphonic (“quad”), home stereo mono sound on film since the 1930s. format promoted in the early 1970s. To enable compatible playback in forerunner of today’s It required two additional speakers in mono cinemas, it was necessary to fit digital sound the rear corners of the listening room, the new stereo soundtrack into the to reproduce two extra channels from same space on the print occupied by n the 1950s, movie prints with specially encoded program sources. the traditional mono track. Experi- magnetic stripe soundtracks pro- I vided the first multichannel sound Because the existing home stereo ments showed that two tracks, treated ever heard by the public. 70 mm prints media had only two channels and with Dolby A-type noise reduction, (A), for example, featured six tracks, could not easily accommodate more, could give excellent fidelity. But originally configured as five identical several schemes were developed to trying to squeeze in more than two channels across the front plus a sur- encode the basic two channels with tracks raised noise to an unacceptable round channel to the sides and rear of additional sound information. Most level, even with noise reduction. the auditorium (B). As screens became smaller, reduc- were based on matrixing techniques Two channels, however, were not ing the need for five screen channels to that enabled folding extra channels enough for movie stereo. Movie carry dialogue, Dolby Laboratories into the two regular channels by screens are so wide that as well as proposed the configuration shown recording them with different the usual left and right channels, above, which has been standard since relative phase. a separate center channel and speaker the late 1970s: left, center, and right main screen channels (1,3,5), one Quad failed to capture much of a are required to localize dialogue for surround channel (6), and two low- market. For one thing, there were viewers seated off-center. In addition, frequency-only “bass extension” chan- several incompatible encoding/ “stereo” and “surround” had become nels (2,4). decoding systems, which created synonymous to most of the film Dolby also developed a technique consumer confusion. For another, industry, so a surround channel was enabling 70 mm prints to carry two surround channels, instead of the usual producers and recording engineers also a must. Thus a way had to be one, at the option of a film’s producers. couldn’t agree on how to best use the found to encode just two physical This “stereo surround” 70 mm format extra channels. And most significant tracks on movie prints with four thus became the forerunner of today’s of all, few consumers perceived any channels of information: left, center, “5.1”-channel Dolby Digital surround real advantage from the format. right, and surround. format with its three front channels, two surround channels, and low-frequency Quad was never associated with The solution was found in the effects channel (see page 5). the multichannel stereo formats used matrixing techniques first tried for 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 quad home stereo, but with the did quite the opposite. Movie atten- Stereo comes to video playback channels configured in the dance actually increased with the cinema stereo norm—left, center, growth of the prerecorded video As the video revolution got right, and surround—and with the cassette. Films that proved popular in underway, consumers were not only addition of sophisticated new elec- theatrical exhibition proved just as accustomed to high-quality stereo tronic steering techniques. popular for home viewing, and in sound from their music systems at The Dolby stereo optical format some instances, films that did not do home, but were also becoming used proved so practical that today there well at the box-office fared better in to high-quality stereo sound in the are tens of thousands of cinemas video release. cinema as the Dolby multichannel worldwide equipped with Dolby The video cassette was not optical soundtrack format spread processors, and for many years the only element of the video revolu- throughout the film industry. virtually every major title has been tion. More homes than ever were While at first the video cassette released in the format (even today, connected to cable systems, providing offered only relatively low-fidelity movie prints with digital soundtracks viewers with still more program mono sound, machines and prere- have Dolby analog soundtracks as sources (and the film industry with corded tapes with stereo sound were well, to ensure compatible playback still more program producing oppor- soon offered, first by means of linear in all cinemas). What’s more, the film tunities). The laser disc, the highest- soundtracks and then by the “HiFi” industry experienced a kind of quality home video program source technology.

Load more