The principle and history of Dolby surround sound

                           The principle and history of Dolby surround sound

Surround sound comes from movies, and its appearance is very popular among film and television companies and audiences. On the basis of the development of surround sound in theaters, Dolby Laboratories has developed a home surround sound system. Or the living room becomes a theater, even in a small space of more than ten square meters, you can feel the audio-visual effects in the theater.

The core equipment of the home theater system is the Dolby Surround Sound Decoder, which is an audio device that uses the 424 analog matrix codec technology developed by the Dolby Institute. ) and rear (S) audio signals in four directions are encoded and mixed into two channels during recording. When replaying, the encoded two-channel composite signal is restored to the 4-channel stereo before encoding through the decoder. 4-channel stereo can produce three-dimensional stereo effect, with a strong sense of presence.

The first generation of home surround sound system developed by the Dolby Institute in 1982 is Dolby Surround, which can only provide left, right and surround 3 channels, with poor separation and directivity, and each channel is balanced. It is manual, the frequency response of surround sound is within 7000Hz, and the delay time is fixed at 20ms and adjustable at 15-30ms.

In 1987, the Dolby Institute launched the second-generation home Dolby Surround Sound System Dolby Surround Pro-logic (Dolby Professional Logic Surround Sound or Dolby Pro-Logic Surround Sound), which added a center channel and adopted directional enhancement technology to increase the The separation of the front and surround channels is improved, the sense of presence is better, and the separation and directionality are significantly improved. It can test the noise and control the level, and automatically control the balance of each channel. The central channel of the system has three modes: "Normal", "Phantom" and "Wide", which have strong adaptability. Due to its mature technology and high cost performance, the system has achieved great success and was once the mainstream of home theaters.

Dolby Pro Logic decoding can be done either analog or digital, the result is the same, there is no optimal mode. Therefore, when evaluating each surround sound decoder, it must be carried out from the two aspects of sound quality and economy. THX (Tominson Holman Xperimant) is a standard established by Lucas film Ltd on the basis of Dolby Pro Logic Surround Sound, which puts forward new requirements for back surround channels and subwoofer channels. , The rear surround channel is analog stereo, and the reproduction of bass is enhanced. Therefore, a series of signal processing systems have been developed to make the Dolby system reach the THX standard.

In 1994, the Dolby Institute launched the all-digital Dolby AC-3 system (Dolby Surround Audio Coding-3), the Dolby Digital Surround Sound System. Its special feature lies in its 5.1-channel, front left, center , 5 full-band channels, front right, rear left, and rear right, denoted by 5, and the subwoofer channel with only low frequency band is denoted by 0.1, and its two rear surround channels are full-band stereo, independent subwoofer The sound channel makes it more realistic than the THX system, and the 6 independent channels are enough to achieve the effect of being in the environment, making the home theater enter a new and higher audio-visual realm, which is the mainstream of the development of the surround sound system. .

In 1996, the dts (digital theater system) home theater researched and developed by the American Digital Theater System Technology Research Corporation adopts another digital surround multi-channel system. dts adopts coherent acoustic digital audio processing technology to provide a more unique coding and processing method, which can completely restore the original audio information. Due to its unique performance and characteristics, it has been recognized as the 5.1 channel of the Dolby digital system. The standard way of multi-channel surround sound.

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In June 2000, the Dolby Institute launched a new generation of Dolby Surround Pro-logic Ⅱ, a matrix surround sound system that conforms to 5.1 channels and provides 5 full-band channels, which is not only suitable for playback Various multi-channel programs, and can also process any two-channel program as multi-channel, regardless of analog or digital recording, you can choose the appropriate mode for processing. This technology greatly improves the sense of space, direction and sound field stability, and expands the sweet spot. General DPL II has two modes: Movie (movie) and Music (music).

The Dolby Digital surround sound system has a total of 5.1 completely independent channels. Except for the front left, middle and right channels and the rear left and right channels, the remaining one is either a full-band subwoofer or a 0.1 channel. Therefore, the sound image positioning, phase characteristics and sound field reproducibility are superior, and it is easy to obtain a sound effect similar to that of a theater in a general home environment. The surround channel of Dolby Digital Surround is full-band stereo, and the bass is used as an independent channel, and the isolation between each channel is higher. The THX standard surround sound is simulated into stereo, and its treble area is corrected and adjusted during production, and a large part of the bass is artificially introduced and strengthened, ignoring its independence, so Dolby Digital Surround Sound The on-the-spot reproduction capability is stronger, more realistic and more vivid than THX. Although Dolby Digital Surround Sound is different from Dolby Pro Logic Surround Sound, its hardware and software are fully compatible, so Dolby Digital Surround Sound is the development of Dolby Digital Surround Sound. mainstream.

The 5.1 channel was recommended by the International Telecommunications Union (ITU) in 1994 as the international standard for "Universal Surround Sound System with and Without Image". It is very important to use the Dolby surround sound decoder correctly. First of all, it is necessary to correctly select the working mode, that is, the center channel mode. The second is to balance the volume of each channel. Usually, you can use the pink noise test in the machine to adjust the volume of each channel until the volume is balanced. The third is to have enough loudness in order to achieve a good sense of presence.