In 1976, Dolby Stereo revolutionised the film industry by placing multi-channel stereo sound in movie theatres creating a more involving experience for the audience. In addition to left and right screen channels, theatres also use a centre channel to sharpen the perspective of on-screen sounds, plus a surround channel played over loudspeakers along the sides and rear of the auditorium to immerse the viewer in ambience and special effects. This technology was then extended to bring multi-channel soundtracks to viewers at home, and was called Dolby Surround.
Dolby Surround / Pro Logic
Dolby Surround is the consumer version of the original Dolby multi-channel analogue film sound format Dolby analogue. Dolby Surround or Dolby Pro Logic is based on basic matrix technology. When a Dolby Surround soundtrack is created, four channels of sound are matrix-encoded into an ordinary stereo two channel sound track by using phase shift techniques. A Pro Logic decoder/processor unfolds the sound into the Dolby 4.0 surround. This consists of left and right, center, and a single limited frequency-range mono rear channel which are matrix-encoded onto two audio tracks. These two tracks are then carried on stereo program sources such as videotapes and TV broadcasts into the home where they can be decoded by Dolby Pro Logic to recreate the original four-channel surround sound experience. A system with out this decoding method would play back the audio as standard Stereo.
Dolby Surround delivers four-channel surround sound via regular stereo VHS, TV and FM radio broadcasts, DVD discs, video games and CDs. Four channels (left, centre, right, and surround) are encoded into two-channel soundtracks and then recovered on playback by means of a Dolby Surround Pro Logic decoder. Dolby Surround is a two-step encode/decode process involving both recording and playback. When a Dolby Surround soundtrack is produced, four channels of audio information, left, centre, right, and surround, are encoded onto two audio tracks using equipment manufactured by Dolby Laboratories. These two tracks are then carried on stereo program sources such as video tapes and TV broadcasts into your home, where they can be processed by a Dolby Surround decoder to recreate the surround sound experience. There are two kinds of decoders: basic Dolby Surround and Dolby Surround Pro Logic. Both recover the surround information from encoded program material and feed it to a pair of surround speakers placed up on the side walls adjacent to the listening area. In a basic Dolby Surround system, left and right front speakers are fed with the entire program in normal stereo without any processing, while the surround speakers are fed with a surround signal derived by a relatively simple passive matrix decoder. As with regular two-channel stereo, the left and right front speakers create a "phantom" centre channel but only for those relatively few viewers seated on centre. By using the same directional enhancement system found in professional Dolby Stereo cinema processors, Pro Logic decoders derive a separate centre channel to keep dialogue and other central sounds firmly localised on the video screen. Pro Logic also supplies higher separation among all four channels and more accurate sound positioning, which along with the centre channel enable a greatly expanded listening area. Dolby Surround Pro Logic is the best way to accurately reproduce the Dolby Stereo theatre experience in your home and will ensure that you hear Dolby Surround soundtracks as the producer intended. The basic Dolby Surround Decoder features passive matrix decoding to derive the surround channel and three output channels, left, right and surround. Surround channel frequency response is limited to 7kHz plus modified Dolby B-type noise reduction. Surround channel time is variable from 15ms to 30ms. Dolby Surround Pro Logic Decoders feature in addition high-separation, active matrix...
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