【正文】 ( L ), the right channel ( R ), the center channel ( C ), surround channel ( S ) of the 4signal, encoded into LT, RT posite double channel signal, replay through the decoder will encoded twochannel posite signals LT and RT reduction for encoding the left, right, in around four, each stem and independent signal, amplified respectively input left, right, center and surround sound speakers. In order to playback symmetry reasons, surround speakers using the left and right surround speakers, respectively, from the output of the amplifier, so the business to Dolby ProLogic surround sound output called channel five. But due to a left, right surround sound speakers connected in a channel, the output is the same as the surround channel information, the essence is still four channel. The business also has six channels and seven channels Dolby Pro Logic AV amplifier. The six track is the central channel two amplifying circuit is respectively connected with the output, in left center speaker and right center speaker. But left, right center speaker connected to a center channel, it is essentially a four channel. Seven channel surround sound channels is divided into four channel output, . left rear surround, right rear surround sound, and adopts four surround sound, which became a seven channel output. But the output of the seven track four surround speakers are connected in a surround channel, also can calculate the output of four sound channels. So with Dolby Pro logic decoder AV amplifier whether five channel output, six channels of output or the seven output channels, is essentially a four channel. Dolby ProLogic surround sound in the left, right, three channel frequency range can reach 2020210Hz, can meet the full range of requirements, but surround channel frequency range is narrow, only 1007000Hz. Dolby E is designed for digital TV broadcast and postproduction and the design of a 畢業(yè)設計（論文）外文資料 5 professional audio coding system. Using the Dolby E, a AES / EBU channel can send up to 8channels of high quality digital audio stream, and also can be loaded Dolby digital control data signals (often called the metadata, including the Dolby digital mono mode, dynamic range, type, output level automatic adjustment of parameters, to ensure that users can correct Dolby digital program ). Dolby E with its advanced coding algorithm and higher data transmission rate, can ensure the digital TV audio signals through as many as 10cycle coding decoding or other editing process, and does not cause quality deterioration. Dolby E audio can be associated with various formats of video signal is a good match, won39。s laboratory developed the third generation of perceptual coding system. Each code system will be a special psychological acoustics ( psycho acoustics ) knowledge and advanced digital signal processing technology bine very well. AC1 initially by the Australian Broadcasting Corporation in 1985 for its DBS system. Perhaps partly because AC1 decoder cost reasons, it appears to be widely applied to other DBS services, satellite munication work and digital wired broadcasting system. According to their different applications, each channel code rate for 220325bit / sec. As an adaptation of delta modulation ( ADM ) in the form of a digital stream, ( datastream) contains information not by audio signal absolute value provided, but by different sampling ( Sample ) value changes identified. By Dolby transform to noise reduction techniques, such as: continuous transformation step and preemphasis can greatly improve the adaptation of delta modulation ( ADM ) basic performance. Dolby AC2advanced adaptive transmission code used in professional audio transmission and storage, which each channel digital rate of 128 or192day / sec. Narrow band multiplicity of frequency control signal program fully adopted the noise masking superiority, resulting in an efficient reduction rate and high signal transparent effect. In other applications, such as: a long distance transmission, real time (realtime ) recording, mixing and adding storage ( ADR ) are very widely used for connecting remote recording studio or film shooting field. AC =3 is also 畢業(yè)設計（論文）外文資料 7 used to connect the BBC Transmitter Room and the Dolby DSTLR system core equipment. AC3 is in the AC1and AC2is developed on the basis of multi channel coding technology, to retain the original AC 2such as window function, exponential transform coding, adaptive bit allocation and many other features, but also a new stereophonic sound channel coding technology strategy for the coupling and rematrix algorithm. In general, the stereo left channel and a right channel signal in the sense of hearing is very similar, there are many repetitive redundancy information, will be the two channel signals bine to be coded, can remove redundant signal and will not affect the original sound quality. Here AC3array low bit rate and an effective means of. AC3PC voice data input, output the pressed digital bit stream. Coding is the first step, using the TDAC ( Time Domain Aliasing Cancellation ) filter the timedomain PC sampling data is transformed into a frequency domain blocks into a series of transform coefficients, each transform coefficient in binary exponential notation, namely an exponent and a mantissa. Exponent part encoded constitutes the entire signal substantially the spectrum, also known as the spectral envelope. Using the spectrum including and shaded by line correlation decision each mantissa bit allocation. Because the bit allocation is adopted i n the anterior / posterior to the hybrid adaptive bit allocation and public bit pool technology, which can make the limited rate in the channel between the different frequency ponents, between the rational allocation of the mantissa。s major consumer electronics manufacturers gro