【導(dǎo)讀】江西理工大學(xué)應(yīng)用科學(xué)學(xué)院。畢業(yè)設(shè)計(jì)(論文)外文資料翻譯

　　

【正文】 ock may contain a number of different possible recognition of noise, such as preecho. That is to say the ear due to time and frequency exists on the shadowing effect in the exponential transform coding is a contradiction, not at the same time, must plan as a whole processing. For the steady state signal, whose frequency varies with time transform slow, in order to improve the coding efficiency, requirement filter has good frequency resolution, which requires a long block。 as for the rapidly changing signal, requires good time resolution, which requires a short block. In the encoder, the input signal after3Hz highpass filter removes the DC ponent, and then through a8kHz highpass filter out highfrequency ponents, with its energy are pared with a preset threshold, in order to detect the signal transient situation. AC3based on the modified discrete cosine transform ( MDCT ) adaptive transform coding ( ATC ) algorithm. Although defined in AC3 standard MDCT transform, but the actual using a N / 4IFFT ( FFT ), plus two simple PreIFFT and PostIFFT as adjustment, in order to achieve a N IMDCT transform. ATC algorithm is an important consideration is based on auditory masking effect critical band theory, namely in the critical band within a voice to another voice signal shielding effect the most obvious. Therefore, dividing the band filter group to have fast enough to ensure that critical band frequency response, and noise attenuation is large enough, 畢業(yè)設(shè)計(jì)（論文）外文資料 8 the time and frequency of noise within the defined in the masking threshold. The AC3 encoder bit allocation technique, has been applied widely on the forward and backward adaptive bit allocation rule. Forward adaptive bit allocation method is the encoder calculation, and the bit allocation information explicitly incorporated into the stream of data bits, and is characterized in that the front end of the encoding process uses auditory model, thus modifying the model the receiving side decoding process has no effect。 the disadvantage of reducing coding efficiency, because of the need to transfer the bit allocation information while occupying a part effective bits. To the adaptive method did not get encoder clear bit allocation information, but from a digital stream in which the bit allocation information, has the advantages of no occupation of the effective bits, thus has higher transmission efficiency. Its drawback is from received data to calculate the bit allocation, if the calculation is too plex to the rising cost of decoder. In addition, the decoder algorithm also with encoder auditory model change. AC3using hybrid backward / forward adaptive bit allocation, in enhancing the rate and reduce the cost of strikes a balance between. AC3 decoder decoding principle basically is encoded by the reverse process, firstly, the decoder must with the encoded data stream synchronization, and then from a data error correction of digital flow separation control data, system configuration, the encoded spectral envelope and the quantized mantissas and other content, according to the sound spectrum envelope to generate the bit allocation information, the mantissa part of inverse quantization, restoring the transform coefficient exponent and mantissa, after synthesis filter banks, the data from the frequency domain to time domain, the final output of the PCM sample signal reconstruction. Through the understanding of AC3, you can see the AC3technology makes full use of the human ear sensory model, according to the different properties of signal, to take the corresponding effective algorithm, achieved at a high quality under the premise of achieving a higher rate for the intended purpose, is a very efficient and economical digital audio pression system. AC3 is the American digital television system of mandatory standard, is the European digital television system remended standard, at the same time, AC3or DVD system of pulsory standards. At present our country is the development and promotion of digital TV system, all have reasons to believe that AC3 technology will have a good prospect of application. Dolby Chun chamber ( About DolbyLaboratoies ) from the analog noise reduction ( analog noisereduction ) to the digital code ( digitalcode ), Dolby has concentrated on rooted in laboratory to ear sound perception based audio processing development. In the process of development, Dolby has always been the emphasis is on the critical listening and tested. Either analog or digital program program, their results are the same, with low cost, greatly improves the efficiency of munication media. In some cases, it also for the improvement of new products, such as: Dolby surround sound ( DolbySurround ) and home theater ( home theater T ) make contribution. The Dolby laboratory consists of the following ponents: investment and Technology Development Engineering Department, occupation audio product design and manufacturing sector, experts the anization and distribution of all over the world in the field of support group. Dolby products from panies located in modern American and British manufacturing plant. Lyrics by the world39。s major consumer electronics manufacturers group。 for each license 畢業(yè)設(shè)計(jì)（論文）外文資料 9 production of the product prototype ( prototype ) test。 examination of worldwide manufacturing facilities。 and an integrated circuit ( IC ) manufacturers in close cooperation ( ( / L more than a dozen and Dolby techniques related to integrated circuit manufacturers have license the production of all kinds of product development ). By Dolby training consultant for world production center to provide advisory services, to help solve the film, video and music broadcast media sound track technical problems. When the technology into the multichannel digital audio field laboratory, Dolby not only in the