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Dolby Digital
Digital
sound
2
4
6
8
10
12
14 MHz
Frequency
Analog
sound
(Monaural)
Video
Dolby Digital
sound
Dolby Digital is a compression format which records
the sound of 6 channels of the theater surround
system (Dolby Digital) on the movie film digital track.
Of the 6 channels, the sub woofer channel is intended
for bass only, and because the frequency range is
smaller than the main channel, it is expressed as 5.1
channel.
Dolby Digital is the name of the Dolby surround multi-
channel digital system that was developed after the
Dolby Surround System and Dolby Pro Logic Surround
System.
The number of movies made using Dolby Digital since
1992 has exceeded 300 and continues to increase.
For compact disc players and laser disc digital sounds,
16 bits are used to sample the original analog audio
waveform and sampling is carried out 44,100 times
every second. However because an enormous
amount of recording signal data is required for the
multi channel system with this method, Dolby Digital
is used to compress the data.
In reproducing audio signals, the smaller the bit
number used, the lower the sound quality. With Dolby
Digital, drop in auditory sound quality is prevented by
using masking technology and digital filtering
technology based on the human auditory
characteristics.
Laser disc format
Laser discs are now available on the market in large
numbers. This means that the recording of different
format audio signals on the laser disc raises the
important question of compatibility with existing
laser discs. Dolby Digital tracks on laser discs record
signals using the space of one analog audio channel
so it will maintain compatibility with existing discs
and players.
As shown in the following figure, the digital audio
sounds of Dolby Digital discs can be played back as
currently done. Analog sounds are played back by
using the other channel without the Dolby Digital
signals for monaural audio signals.
5.1 channel digital
surround track
4 channel analog sound
track (Matrix)
Dolby
Digital
encoding
Dolby Digital for movie films
Techno Tidbits & Problem-solving
1
DTS
DTS has been adopted as a sound recording format in the latest movie theaters since the release of “JURASSIC
PARK” in 1993, and has a good reputation for high quality sound and dynamic surround effects.
In this system, 6 channels of digital sound are recorded on CD-ROM, rather than on the film. DTS adopts a
simultaneous playback format. With a low rate of compression of sound signals and a high rate of transmittance,
a higher sound quality format is produced. Also, unlike the process of recording digital sounds on film directly,
the only components required are a CD-ROM player as might be used with a personal computer and a DTS
processor, and therefore less investment is required than with other formats. For this reason, the format is
being introduced in more and more movie theaters, and is being adopted in home movie software (DVD, LD)
and music software (5.1 channel CD).
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