Techno Tidbits and Problem-solving
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
5.1 channel digital | 4 channel analog | |||||||||||
surround track | sound track (Matrix) | |||||||||||
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Dolby
Digital encoding
Dolby Digital for movie films
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,
In reproducing audio signals, the smaller the bit number used, the lower the sound quality. With AC- 3, 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.
Analog sound |
| Dolby Digital |
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(Monaural) |
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Digital |
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| Video |
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sound |
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2 | 4 | 6 | 8 | 10 | 12 | 14 MHz | |
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| Frequency | |
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 sub woofer channel is also called Low Frequency Effect (LFE).
The sub woofer channel can be used as desired to enjoy strong bass sounds.
The table on the next page shows the comparison with Dolby Pro Logic Surround effects.
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