Additional Information
Dolby Digital
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.
5.1 channel digital | 4 channel analog | |||||||||
surround track | sound track (Matrix) | |||||||||
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AC-3
encoding
In reproducing audio signals, the smaller the bit number used, the lower the sound quality. With
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.
Analog sound | Dolby Digital |
(Monaural) | sound |
| (Monaural) |
Digital | Video |
| |
sound |
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Frequency
2 | 4 | 6 | 8 | 10 | 12 | 14 MHz |
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,
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 (LEF) channel. The sub woofer channel is also called Low Frequency Effect (LFE).
The subwoofer channel can be used as desired to enjoy strong bass sounds.
The following table shows the comparison with Dolby Pro Logic Surround effects.
| Dolby Digital | Dolby Pro Logic Surround |
No. of recorded channels | 5.1 channels (Max.) | 2 channels |
No. of playback channels | 5.1 channels (Max.) | 4 channels |
Playback channel structure | Front Left, Front Right, Center, Surround Left, | Front Left, Front Right, Center, |
| Surround Right, Sub Woofer | Surround |
Sound processing | Digital discrete processing | Analog matrix processing |
Rear (Surround) high | 20,000 Hz | 7,000 Hz |
frequency playback limit |
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Other | • 5.1 completely independent channels |
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| • High dynamic range |
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| • Stable position, high phase characteristics, and |
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| advanced surround effects reproduction |
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| • High efficiency |
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| (Compression rate of about |
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43
<ARB7192>
