On Surround Sound System

Dolby Stereo, Dolby Surround

This is the coding and decoding method developed by Dolby Laboratories established by Ray Dolby in London in 1965, and is widely used by professional cinemas. It is called the Dolby Stereo system in a professional movie theater, and the corresponding home software code is called Dolby Surround. Both are analog systems with three channels: front left, front right, and rear surround channels (including mono).

Dolby Pro Logic

This is currently the most common surround sound mode on all AV amplifiers, and almost all of the tapes and DVDs at home can be seen. Dolby Pro Logic is specially designed for decoding Dolby Surround, which is specially designed to improve the positioning of the central dialogue of home AV systems. Dolby Pro Logic can be regarded as an enhanced version of Dolby Surround. In addition to the concept of adding a middle channel, Dolby Pro Logic has also raised the position of the middle channel to the same position as the main channel. In fact, for home cinema systems, the status of the middle channel is sometimes higher than the main channel, which will be more clear on Dolby Digital, which will be mentioned later. In addition, the so-called Phantom mode is also provided, the so-called "virtual middle channel". This means that even if the system is not equipped with a mid-channel speaker, it can still highlight the sound in the middle virtually. Dolby Pro Logic has a total of four channels: front left, front right, surround back channel, and center channel.

Dolby Digital (Dolby Surround AC-3)

Dolby Digital, also known as Dolby Surround AC-3, is the home version of Dolby Stereo SR-D, the all-digital music system for movies designed by Dolby Laboratories. AC-3 is the abbreviation of Audio Coding 3, literally translated as the third generation of audio coding, is a set of audio compression technology. Dolby Surround AC-3 is a new technology developed for the movie multi-channel surround system. In order to greatly reduce the file size of the bit signal, Dolby Surround AC-3 applies destructive compression technology, which can also be called sensory encoding. The so-called destructive compression means that once compressed, it cannot be restored to its original appearance, but if the loss is some insignificant signals, the purpose of greatly reducing the file size can be achieved. In order to accommodate the existing movie theater playback equipment, Dolby Surround AC-3 still records sound signals on film negatives, uses optical means to read digital signals, and then processes them into independent multi-channel signals through Dolby Surround AC-3. Dolby Surround AC-3 has a total of 5.1 channels: five channels including front left, front right, center, right rear surround, and left rear surround, all of which are stereo (Stereo), plus a 3Hz-120Hz The ultra-low frequency channel, so commonly known as 5.l channel.

DTS

DTS (Digital Theater System) is an all-digital multi-channel system for movies developed by Digital Theater System in the United States. It is called DTS for both home and professional use. It is also 5.1 channel. DTS is just like AC-3, in order to save 5.1 channel information in the limited space of movie film, information reduction compression and encoding are also done, but the two systems have different compression encoding methods and principles , AC-3 uses a substantial reduction of the theoretically weak sound that the human ear cannot hear to achieve audio reduction; while DTS uses the method of increasing the digital space rate to calculate the full load reduction bit rate of the information, which retains More weak information. Generally speaking, the average information compression rate of AC-3 is as high as 12: 1, and the information transmission rate (data rate) is only 384kbps to 448kbpS per second, while the average information compression rate of DTS is only 3: 1, and the transmission rate is 1.14kbps per second. Up to 1.500kbps is three to four times that of AC-3. With these technologies, the facsimile of DTS is better than AC-3.

THX

THX is a movie theater playback standard proposed by the American director George Lucas. Its purpose is to improve the sound quality of the movie sound in the movie theater, so that the audience can fully feel the director's attempt to express. Therefore, it has quite strict regulations on the space of the movie theater and all audio equipment, and even the brightness of the screen when playing. There are certain requirements on the screen, and after the cinema is issued a THX license, it must be reviewed every six months to avoid aging of the equipment Not up to standard. The THX specification was later extended from the cinema to home-use equipment, which has the same strict specifications as the cinema. Currently, many manufacturers have produced audio-visual equipment that meets the THX standard. A set of AV system composed entirely of THX specification equipment should be able to achieve the following effects:

1. Treble and bass of the whole frequency band.
Second, the sound is more smooth and natural.
3. Lowest bass distortion in the hearing range.
4. Clearer vocal positioning.

Generally speaking, if the equipment that can get THX certification is very expensive, and most of them have to be matched with Hi-End audio equipment, they can often exert their effects. Therefore, home audio and video systems with THX effects are usually expensive. (Note: THX is a standard and not a piece of equipment. It is different from Dolby Digital, DTS, Dolby Pro Logic, etc. THX is only attached to the surround system mentioned above, the purpose is to enhance its sound effect).

Ambient sound list

At the end of the article, let's talk about S / PDIF again, so as to avoid beginners from confusing several concepts.

S / PDIF

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