【正文】 Dolby A type noise reduction system. Initially used only recorded classical music, when multitrack recording technology promotion, will be more widely applied. Soon, the whole world of professional and nonprofessional begin to Dolby with high quality recording together. With the hope that Dolby will be present and noise reduction technology for civilian recorder voice rising, in an American mercial tape recorder manufacturer KLH pany 39。 with Dolby 39。 DTS usually use much larger bit rate 1536bps. If other conditions are the same, is a bit more quality is better, this assertion is wrong? Unfortunately, the answer to this question is not so easy, because the Dolby Digital ( abbreviated as DD ) and DTS data pression circuit is different. For example, a coding efficiency very low signal, even if the bit rate is very high, also just wasted bits and disc space, but does not improve sound quality. Once a system is said to be transparent, increase the bit rate without causing it to improve the sound quality. In addition because the DTS bit rate higher than Dolby, need takes up more space, if the DVD disk capacity constraints, may produce adverse effects on image quality, or to increase the additional cd. Dolby ProLogic surround sound ( Dolby Pro Logic ) is Dolby developed a surround sound system. It is the four track stereo recording by a specific encoding means for the synthesis of two channel, the original left channel ( 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(shè)計(jì)（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 current version supports frame rate ( NTSC standard, PAL25FPS ),20bit length and 48kHz sampling frequency of the audio signal, a future version will support25FPS,16bit or24bit audio signal. AC3 transmission form AC3 based transmission system into a more extensive application field is feasible in technology. At the end of the century before, several AC3 based application technology into mercial production. High definition television ( HDTV ) is declared using a AC3 code first application technology. Grand Alliance has selected the United States developed this technique. For its high definition television system with digital surround sound and in 1996Atlanta Olympic Games for the first time as media. Because the AC3effects and can be associated with high definition television matches the standard features of digital cable TV system, therefore, is a natural candidate for AC 3. The first test transmission was 1994year. Due to the current available programs can use a single sound, stereo can also use with matrix ( matrix surround ) stereo, therefore, a AC3dual channel decoder for has been developed. And when the multichannel digital program for transmission, high function converter ( converter ) will create a synthetic stereo downward 畢業(yè)設(shè)計(jì)（論文）外文資料 6 mixing effect. Always as home theater the highest quality image source DVD ( (LD ) as Dolby surround digital multichannel audio examples show. Using AC3bit stream ( bit stream ) alternative FM channel in a channel, so that the stereo pulse code modulation ( PCM ) digital a udio soundtrack with FM mono cooperate with each other, so that it can be patible with existing any player. With cable, DBS and DAB is realized by AC3spectrum effect, quality and multi channel features a