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Surround sound system
Sunday, 14 January 2007
A surround sound system is a sound reproduction system that uses multiple channels and speakers to provide a listener with simulate placement of sound sources. Typically, the listener is positioned between multiple speakers. By playing a sound at different intensities through one or more of the speakers, the sound is positioned with respect to the listener. In this way the listener may be "surrounded" with sound sources to create a more interesting or realistic listening experience. The evolution of sound reproduction began with a simple sound source such as a horn loudspeaker acoustically coupled to a rotating cylinder which carried physical impressions of sound scribed into its surface. The emitted sound was very localized, propagating from the horn with a directional aspect oriented along the horn throat axis. Improvements in the quality and realism of sound reproduction have steadily been made during the past several decades. As speakers became more sophisticated, stereophonic features were added in combination with use of multiple speaker systems, generating left and right or side-to-side dynamics to sound reproduction. Stereo (two channel) recording and playback through spatially separated loud speakers significantly improved the realism of the reproduced sound, when compared to earlier monaural (one channel) sound reproduction. More recently, the audio signals have been encoded in the two channels in a manner to drive four or more loud speakers positioned to surround the listener. This surround sound has further added to the realism of the reproduced sound. Modern surround-sound systems capitalize on diverse speakers to generate both stereophonic output, as well as synchronized shifting of isolated sounds to individual speakers disposed around the listener. Multi-channel (three or more channel) recording is used for the sound tracks of most movies, which provides some spectacular audio effects in theaters that are suitably equipped with a sound system that includes loud speakers positioned around its walls to surround the audience.

Surround sound processing is a technique in audio engineering wherein a stereophonic pair of signals from a source such as prerecorded audio or live transmissions of audio signals, with or without video, is processed to yield a set of signals for the purpose of feeding several loudspeakers placed around the listening area, so as to give an impression of spatially surrounding the listener with the sounds, particularly any ambience, and/or broadening the sound field to wrap around the listener. Because of the physiology of the ear, human hearing is amazingly capable of assigning a directional aspect to sound. This ability provides a continuous flow of information to the brain, supplying data which is assimilated in defining an individual's position and environment within a three-dimensional framework. In addition, low and high frequency sounds which are heard by a listener arrive via multiple paths. In addition to a direct, simultaneous arrival, high and low sounds often are reflected or bounced off walls and objects prior to arriving at the listener's ears. Depending upon their source and line of transmission, sounds may be characterized as direct, reverberations, and indirect late reverberations which may be measured with digital computing equipment. The multiple arrival of sound causes perceptibly phase shifted signals. Modern surround-sound systems simulate a desired three-dimensional environment by directing sound to the listener from various orientations, including front, side, back, floor and ceiling propagation. The surround sound process involves encoding two stereophonic channels with multiple channels of audio information by mathematical manipulation of frequency and phase information. The two channel encoded audio information is then decoded through a surround sound processor and directed to a plurality of loudspeakers thereby presenting multiple channels of audio information to a listener. Proper speaker placement allows the listener to perceive audio signals emanating from the front, rear, or side depending on the speaker placement. Popularly, a 5.1 channel surround system is used as a reproduction system. The 5.1 channel surround system includes an apparatus which serves as a source and speakers for 6 channels in the maximum. The speakers include speakers disposed at left, right and central positions forwardly of the listener, speakers disposed at left and right positions backwardly of the listener, and a subwoofer speaker for applying a heavy bass boosting effect.

There have been made many developments in the surround-sound generation technology that gives more satisfactory stereophonic sound effect to a listener than a conventional two-channel stereophonic sound. A typical surround sound signal includes at least left front, center front, right front, left rear and right rear signals. Reproduction of multichannel audio signals is performed with a front center speaker, a surround left speaker, and a surround right speaker in addition to speakers arranged at the front left and the front right side to the listener. In order to implement effective surround-sound experiences, conventional sound systems include many speakers, positioned around a room perimeter, including floor and ceiling. Typically, low frequency range woofers are located at the front of the room, or under the floor. Because these low frequency speakers have less directionality, their placement at a particular location in a room is not problematic. With high range frequencies, the directional aspect of sound propagation is enhanced. Tweeters can readily be detected as to source or orientation. Surround-sound systems supply these higher frequencies from smaller speakers which are dispersed at the sides and back of the room, enabling their beaming properties to simulate sound emanating from multiple directions as if in a natural environment. Modern day stereo audio reproduction systems provide sound reproduction more realistic than monophonic systems because two soundfields are utilized to give the listener an impression closer to that of alive performance which generates sound from multiple sources located at multiple points in space relative to the listener. The availability of DSP and improved filtering algorithms has made it possible to create a phantom sound source in almost any location using just a single pair of loudspeakers typically located in front of the listener. Recently, package systems have been introduced that comprise five physically small loudspeakers plus a larger subwoofer. The five small loudspeakers interfere less with room decor and the subwoofer location is flexible because of its frequency range. Recent stereo reproduction systems provide more realistic sound reproduction than ever before by utilizing multiple channels to separate low frequencies from high frequencies.

Surround sound audio is growing rapidly due to the proliferation of home theaters, digital television, surround sound music, and computer games. The roots of surround sound audio are in the motion picture industry. A multi-channel surround system is employed in a movie theater and allows reproduction of surround sounds full of presence together with a video image reflected on a screen of a large size. Typical theaters have three speakers in the front which provide stereo along with a center channel for dialog, and two speakers in the rear for special effects and ambient sounds. Home audio/video entertainment systems have become very popular today. Many people have installed complete A/V systems at their own homes to make so called "home theaters" for enjoying individualized entertainment. A home theater entertainment system typically includes a large screen or projection television (TV) set, a multiplicity of audio/video components and a speaker system. The multiplicity of audio/video components may comprise an audio/video receiver which serves as the control center of all other audio and video components of the entire audio/video system. The audio components may include a compact disc (CD) player, a digital video disc (DVD) player, audio/visual (A/V) receivers, tuners, equalizers, headphones, satellite speakers, center channel speakers, woofers, and/or subwoofers disposed in a fixedly mounted rectanguloid housing. The video components may include a video cassette recorder (VCR) and a laser disc (LD) player. In order to regenerate a surround sound field space, a source and a system for reproducing the source are required. The source may be a video disk such as a DVD (digital versatile disk), a DVD-ROM (digital versatile disk read only memory), a cable system, a satellite broadcast or a digital television broadcast, and also an Internet broadcast may be applicable. The listener usually listens to surround sounds while observing, at the center surrounded by the speakers, a video monitor installed in the proximity of the speaker for the forward center.

The ability to process audio information has become increasingly important in the personal computer (PC) environment. With the proposal of increased video and audio applications in multimedia personal computers, a user can potentially use the computer to control the television, telephone and home stereo as well as connect signals from cable television links, satellite TV and various other video/audio sources such as compact disc (CD) players, VCRs and digital versatile disc (DVD) players to the home entertainment system. With the introduction of DVD, CD and other audio sources into the PC market, there is a trend to develop new game titles and movies which deploy the surround sound format having three or more audio channels in order to give a realistic, surround sound environment to the PC user. Speaker systems with integral amplification electronics provide simple, compact audio transducers for multimedia personal computers. These multimedia computer speaker systems typically include pairs of wide-band speaker drivers mounted in separate housings with amplification electronics incorporated into one or both housings. Because compactness is desirable, small, wide-band speaker drivers are commonly used. Some multimedia computers include four-channel surround sound systems. A four-channel multimedia computer audio sub-system includes a multimedia computer speaker system with four wide-band audio transducers or speakers, and typically a sub-woofer audio transducer or speaker. The four wide-band speakers receive four different audio signals or channels. A typical encoded surround sound signal may utilize coding schemes such as Dolby AC-3, Sony Dynamic Digital Sound, Digital Theater Systems, or the like. The most well known surround sound mode is presented by Dolby Laboratories marketed under the trademark Dolby Surround Sound. Dolby encodes video and film soundtracks for active decoding of the soundtrack thereby delivering five discreet channels of audio.

As the audio technology progresses, digital applications are increasingly sophisticated as improvements in sound quality and sound effects are sought. One of the key components in many digital audio information processing systems is the decoder. The device that plays back recorded audio signals through the speakers to achieve the surround sound effect is called a surround sound decoder. Generally, the decoder receives data in a compressed form and converts that data into a decompressed digital form. The decompressed digital data is then passed on for further processing, such as filtering, expansion or mixing, conversion into analog form, and eventually conversion into audible tones. Surround sound decoders are a common device in commercial movie theaters since surround sound is especially well-suited as a movie audio effect. By using surround sound along with a theater's large projection screen, an audience can be more completely immersed in the movie experience. In the home environment, the decoder is usually incorporated in, or is an accessory to a videocassette player, videodisk player, or television set/video monitor. With the growing popularity of home entertainment centers, many consumers are creating high quality theater-like image and audio centers within their homes. Surround sound audio capability is one of the advanced features installed in such entertainment centers. Surround sound processors are normally used to decode surround sound audio signals which are recorded on the sound tracks of video cassettes and discs. A surround sound processor operates to enhance a two-channel stereophonic source signal so as to drive a multiplicity of loudspeakers arranged to surround the listener, in a manner to provide a high-definition soundfield directly comparable to discrete multitrack sources in perceived performance. Stereo audio signals are decoded into in-phase signals and out-of-phase signals. The in-phase signals will be sent to at least one center speaker. The out-of-phase signals will be sent to at least one rear speaker. Surround sound processors will also enhance the imaging of audio recordings. Surround sound processors may be divided into two main classes, fixed matrix or passive, and variable matrix or active types.