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Dolby Digital

Digital

sound

2468101214 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.

Comparison with Dolby Pro Logic

Surround

Dolby Digital is also known as the 5.1 channel

system. It is equipped with 5 channels (front left,

front right, center, surround left, surround right) in

the frequency range from 20 Hz to 20 kHz and an

independent Low Frequency Effect (LFE) channel.

The subwoofer channel is also called Low

Frequency Effect (LFE).

The subwoofer channel can be used as desired to

enjoy strong bass sounds.

5.1 channel digital

surround track

4 channel analog sound

track (Matrix)

Dolby

Digital

encoding

Dolby Digital for movie films

Techno Tidbits & Problem-solving

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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