 Dolby Surround
The Dolby Surround process includes encoding four channels of information--Front Left, Center, Front Right, and Rear Surround into a two channel signal. A decoding chip decodes the four channels and sends them to the appropriate direction, the Left, Right, Rear, and Phantom Center.
The result of Dolby Surround mixing is a more balanced listening environment in which the main sounds come from the left and right channels, the vocal or dialog radiates from the center phantom channel, and the ambience or effects information comes in from behind the listener.
The sound encoded with this process has a more natural feel, with better acoustical cues. In movie soundtracks the feeling of sounds moving from front to rear and left to right adds more realism to the viewing/listening experience by placing the viewer in the action. Dolby Surround is easily helpful in both musical and film sound recording.
Dolby Digital
Dolby Digital 5.1 adds both accuracy and flexibility by adding stereo rear surround channels that helps sounds to radiate in more directions. Dolby Digital encoding/decoding requires the same power output and frequency range as the main channels. Dolby Digital encoding on DVDs, Laserdiscs, and Satellite programming is very widespread and has established this format in the marketplace. Since Dolby Digital includes its own encoding process, you need to have a Dolby Digital receiver or amplifier to decode properly the signal, which is transferred from a component, such as a DVD player, via either a digital optical connector or digital coaxial connector.
Dolby Digital EX
In Dolby Digital, much of the surround sound effects move from the front or sides towards the listener. Nevertheless, the sound loses some direction as it moves along the sides to the rear, making a perfect directional sense of sounds from moving objects or panning across the room difficult. By placing a new channel directly behind the listener, panning and positioning of sounds radiating from the sides to the rear are much more perfect. Also it is possible to originate sounds and effects from the rear more precisely with the help of additional rear channel. This put the listener even more in the center of the action.
Dolby Pro Logic II
Dolby Pro-Logic technology can create a "simulated" 5.1 channel surround environment from a 4-Channel Dolby Surround signal. Although not a seperated format, such as Dolby Digital 5.1 or DTS, in which each channel goes though its own encoding/decoding process, Pro Logic II makes an efficient use of matrixing to deliver an adequate 5.1 demonstration of a film or music soundtrack. With improvement in technology since the original Pro-Logic scheme was developed over 10 years ago, channel separation is more distinct, giving Pro Logic II the character of a discrete 5.1 channel scheme, such as Dolby Digital 5.1.
Dolby Pro Logic IIx
Dolby Pro Logic IIx is a more recent variant of Dolby Pro Logic II. Dolby Pro Logic IIx expands the extracting capabilities of Dolby Pro Logic II, including its preference settings, to 6.1 or 7.1 channels on Dolby Pro Logic IIx-equipped receivers and preamps. Dolby Pro Logic IIx serves to send the listening experience to a greater number of channels without having to remix and reissue the original source material. This makes your record and CD collection easily adaptable to the latest surround sound listening environments.
SRS: Tru-Surround
Dolby Labs and DTS aren't the only forces in surround sound technology, SRS Labs also has innovative technologies that can enlarge the home theater experience.
Tru-Surround is a sound-scheme that can take multi-channel encoded sources, such as Dolby Digital, and create the multi-channel surround effect by just using two-speakers. The result is not as exciting as true Dolby Digital 5.1. Nevertheless, with many consumers reluctant to fill their room with six or seven loudspeakers, Tru-Surround helps to enjoy 5.1 channel sound within a normally-limited two channel listening environment.
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