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The Company's Founding |
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Dolby and the Digital Age
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Dolby® SR, the most powerful Dolby technology for analog
recording, dramatically
increased the dynamic range of such formats as film soundtracks and professional analog tape
recording (1986). |
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Dolby's reputation as a leader in audio technology was greatly enhanced in 1986 with the introduction
of a powerful new system, Dolby SR (spectral recording), intended to bring analog recording into the
digital age. By combining both the fixed and sliding band technologies invented for the earlier noise
reduction systems, Dolby SR improved the performance of existing professional analog recorders to the
point where they equaled, and in some respects surpassed, very costly digital recorders. This proved
a boon to many professional recording facilities unable to afford digital equipment.
Just as important, Dolby SR improved film sound significantly, both in the mixing of soundtracks and
in the soundtracks themselves. Today the Dolby SR encoded analog optical soundtrack, with its ultra-low
noise and distortion, is the state-of-the-art in analog film sound, and is used for the vast majority of
releases, including those that also have digital soundtracks. Dolby SR also fostered a new, more powerful
NR system for consumer cassette recording, Dolby S-type.
Concurrent with developing these advanced analog systems, Dolby Laboratories began researching digital
audio in 1982. The primary goal was, and remains, to reduce the amount of data required to transmit and
store high-quality digital audio. Without such perceptual coding, as reduced bit-rate digital audio systems
are sometimes called, digital audio's appetite for bandwidth would severely limit its potential.
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Dolby Laboratories' first digital product, the DP80
encoder unit, was based on
Dolby AC-1, the company's first digital audio coding technology (1985). |
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The first Dolby digital coding system, Dolby AC-1, was introduced in 1984. It was adopted beginning in
1985 in a number of direct satellite broadcast and cable distribution systems. Encoding units are
manufactured by Dolby Laboratories, while the decoder is licensed. Dolby AC-2, a more sophisticated
system providing full professional quality audio, was introduced in 1989. It has since become particularly
popular with music recording and film studios for interconnecting widely separated facilities via
economical ISDN lines for remote monitoring, dubbing, and other applications. Dolby AC-3, now known
simply as Dolby Digital, was introduced in 1992; it was developed specifically for multichannel
applications, including film sound and digital surround sound in the home.
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Dolby Digital (AC-3) is a multichannel digital audio coding technology
first used for cinema sound (1992). Today it is also used to bring multichannel sound into
the home via a wide variety of digital formats, including DVD, DTV, digital cable, and DBS.
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Dolby's move into the world of digital audio has been facilitated by its many years of research into
psychoacoustics and noise reduction, which is in essence a form of analog audio coding. For example,
as the amount of available digital data for audio goes down, background noise goes up. Dolby's digital
technologies use that apparent weakness to its advantage, by deliberately allowing the noise level to
go up to a point at which it is just hidden, or masked, by audio signal itself.
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| Dolby Digital film sound uses the 5.1-channel format,
with five-full range
channels (Left, Center, Right, Left Surround, Right Surround) and a sixth, bass-only
Low-Frequency Effect (LFE) channel. |
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Once noise is below a certain threshold, it is inaudible—so there is no point in further reducing it.
However, that threshold varies in different parts of the audio spectrum, called critical bands, and also
varies with how loud the signal is in each band at any given moment. Both Dolby AC-2 and Dolby Digital
constantly monitor how loud the signal is in each of these critical bands, and code it with just enough
data to keep the noise just below that band's threshold of audibility. Dolby Digital also compares what's
happening in these bands in different channels, so that sounds in one channel can provide masking for
noise in another. The net result of this complex process is a dramatic gain in efficiency: Dolby Digital
makes it possible to transmit or store six audio channels with less data than is needed for just one
channel on a CD.
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| Home theaters equipped with multichannel Dolby Digital
decoders provide the
same 5.1-channel configuration as digital cinema sound. |
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Dolby Digital and the Future
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The Dolby Digital technology that makes it possible to
place a multichannel
digital soundtrack on 35 mm release prints also brings multichannel sound into the home via
consumer digital formats. |
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The first application for Dolby Digital was film sound. Its bit-rate reduction made it possible to put
a completely separate optical soundtrack on 35 mm release prints (between the sprocket holes). With this
space savings, Dolby Digital movie prints can have an analog Dolby SR optical track in the usual location
to ensure compatibility with all theatres. Dolby Digital is now also used for laser discs, DVDs, ATSC digital
broadcast TV, digital cable systems, and satellite systems.
When it comes to digital sound with film, on disc, and other consumer formats, Dolby Laboratories faces
considerable competition; however, the company remains unique in its ability not only to develop superior
technology, but also to foster its adoption worldwide by means of its professional equipment manufacturing
facilities, its licensing program, and its film sound program. Add to these advantages a skilled,
dedicated staff and an unmatched reputation for quality, and Dolby Laboratories faces the future with
confidence.
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