| 摘要: | 近年來通訊快速的發展，包括有線、無線、以及網路等等，對於多媒體的檔案，如影像、聲音、圖片等，都需要經過適當的壓縮及編解碼處理，才能夠在有限的頻寬上傳輸。在聲音的壓縮標準上，目前最為普遍使用的就是MPEG-1 Layer 3 (MP3)，然而隨著技術的進步，更高壓縮率及壓縮品質的音訊標準也不斷的被提出，在1994年Moving Picture Experts Group (MPEG) 所提出新一代的音訊壓縮標準MPEG-2 AAC，因為比MP3有更好的壓縮效率及壓縮品質，未來將有可能取代目前的MP3，而以MPEG-2 AAC為基本核心的MPEG-4 AAC也在1998年被提出，使用更多先進的技術來解決壓縮品質及壓縮效率的問題，MPEG-2/4 AAC也將成為繼MP3之後，下一個最廣為被應用的音訊壓縮標準。 目前大部分的音訊編解碼器包括MP3、AAC等都是利用數位訊號處理器(Digital Signal Processor，DSP)為主要的設計基礎，然而由於其複雜的演算法特性，一般設計者皆是從C語言的層次來進行系統的最佳化設計，但是因為無法真正與DSP的硬體架構一起做考量，通常在效能及功率上都會有所折扣。在本系統中將以組合語言的方式來實現MPEG AAC音訊解碼器，並以工研院自主研發之PAC DSP為開發平台，首先我們將從AAC演算法上進行初步的分析，提出快速的演算法達到初步的最佳化，然後配合PAC DSP的特殊硬體架構及指令集，以組合語言的方式做進一步的最佳化，最後實現一個完整MPEG-2/4 AAC音訊解碼器。 With the increased development of communications, including wire、wireless and network etc., all the multimedia files need compression to be transmitted on a limited bandwidth. In digital audio coding, MP3 is the most popular audio compression format in current days. However, with the progress of coding technology, new standards have been proposed which have higher efficiency and higher quality. MPEG-2 AAC, a new standard proposed by MPEG in 1994, has higher compression efficiency than MP3 and has chance to replace MP3 in the near future. MPEG-4 AAC, a newer standard proposed in 1998, which is based on the techniques used in MPEG-2 AAC but added some more efficient tools. Since the properties of higher compression rate and higher quality, MPEG-2/4 AAC will replace MP3 as the most popular audio compression standard. Currently, most audio decoder including MP3, AAC are implemented based on the Digital Signal Processor (DSP). However, since the complex algorithms in audio standards, the designers can usually optimize the decoder in C-level. They cannot consider the DSP hardware architecture and algorithms simultaneously. Therefore, the decoding efficiency is decreased and power consumption is increased. In this project, we will implement the MPEG-2/4 AAC audio decoder on PAC DSP with assembly language. First, we will analyze the decoding algorithms and proposed fast algorithms for the initial optimization. Then, we write assembly for further optimization based on the PAC DSP’s architecture and instruction set. Finally, we will complete the optimized design of MPEG-2/4 AAC decoder. |
