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研究生:陳繼大
研究生(外文):Ji-da Chen
論文名稱:改善MPEG-4音訊編碼之PNS工具
論文名稱(外文):Improvement of PNS Tools for MPEG-4 General Audio Coding
指導教授:杭學鳴
指導教授(外文):Hsueh-Ming Hang
學位類別:碩士
校院名稱:國立交通大學
系所名稱:電子工程系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:英文
論文頁數:65
中文關鍵詞:壓縮音訊雜訊壓縮
外文關鍵詞:compressionaudioMPEGAACPNSnoise substitutionperceptual noise substitutionnoise
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MPEG-4是ISO/IEC MPEG (Moving Picture Expert Group)所訂定最新的多媒體壓縮標準。一般音訊 (General Audio)是它的音訊部分。一般音訊可以選擇從12kbit/s ~ 64kbit/s的位元率(bitrate)來編碼雙聲道,甚至在壓縮5聲道音樂時只需320kb/s即可達到‘無法分辨原始訊號及壓縮後訊號’的品質。一般音訊的基本架構與MPEG-2 AAC (Advance Audio Coding)(前一代MPEG音訊壓縮標準)相同,另外它加入許多工具(tool)來增加編碼效率。本篇論文將選擇PNS (Perceptual Noise Substitution)工具作為研究的題目,並藉由適當的使用這個工具以增加壓縮效率。
PNS是一種有效的壓縮聲音中類雜訊部分(noise-like components)的方法。由於標準規定了資料的格式及解壓的方式,因此我們所能改善的只有選擇PNS參數及是否使用PNS。另一方面,我們發現PNS所需的額外資訊(overhead)如果不適當的減少的話,當位元率(bitrate)低時,它將會佔掉太多的位元導致編碼效率的下降。因此,我們提出一個有效的偵測聲音雜訊部分的方法,並在位元分配(bit-allocation)中加入決定是否使用PNS的判斷以減少PNS所需的額外資訊。
實驗結果指出新的的方法在壓縮類雜訊部分可以省下不少位元,藉此,音訊壓縮的效能將可以增加。

MPEG-4 is the latest multimedia compression standard defined by ISO/IEC MPEG (Moving Picture Expert Group). Its audio part, GA (General Audio), aims at data rates from 12kbit/s to 64kbit/s for encoding a pair of stereo channels to 320kb/s for encoding five-channel audio with ‘indistinguishable quality’. The basic structure of MPEG-4 GA is the same as that of the MPEG-2 AAC (Advance Audio Coding), the previous MPEG audio standard. Yet, it adds in several tools to improve its coding efficiency. This thesis selects one of the new tools, PNS (Perceptual Noise Substitution), as the research topic. We try to improve the audio coding efficiency by the proper use of this tool.
PNS is an efficient method of coding the noise-like components in an audio signal. Although the data format and the decoder operation of PNS have been standardized, the method of choosing PNS parameters and the decision of using PNS or not are not standardized. In addition, we find that if we do not reduce the overhead of PNS, it would take up too many bits and thus decrease the coding efficiency. Therefore, we propose an effective and efficient procedure that detects the noise part of sound, and add a decision rule inside the bit-allocation loop to decide if PNS should be used.
Simulations indicate that the new procedure saves bits in coding the noise-like components and thus may increase the overall audio coding performance.

中文提要 i
英文提要 ii
誌謝 iii
目錄 iv
Tables v
Figures vi
Chapter 1 Introduction 1
Chapter 2 Basic Concept of Audio Compression 3
2.1 Time-frequency analysis 3
2.1.1 Subband Coding 3
2.1.2 Transform coding 4
2.1.3 Difference between Subband coding and Transform coding 5
2.2 Human hearing system 6
2.2.1 Absolute Threshold of Hearing in Quiet 6
2.2.2 Critical Bands 8
2.2.3 Simultaneous Masking 9
2.2.4 Temporal Masking 12
2.3 Quality measurement 13
Chapter 3 General Audio in MPEG-4 version 1 17
3.1 Brief History 17
3.2 MPEG-4 Audio Subpart 1: Main 19
3.2.1 Characteristic of MPEG-4 audio 19
3.2.2 New concepts in MPEG-4 Audio (Compared to MPEG-1, -2) 20
3.2.3 Profiles and Objects 21
3.3 MPEG 4 general audio Concepts and its Architecture 22
3.4 Overview of each Tool in MPEG-4 General Audio 28
Chapter 4 PNS Tool 38
4.1 Review of noise-like components coding 38
4.2 PNS in MPEG-4 GA 41
4.3 Our Proposed PNS method 43
4.3.1 Noise-like Component Detection 43
4.3.2 Modified Bit-allocation 48
4.4 Experimental results 52
Chapter 5 Conclusions and Future Work 62
Reference 64
簡歷 65

[1] T. Painter, “Perceptual coding of digital audio”, Proceedings of the IEEE, Vol. 88, No. 4, April 2000
[2] P. Noll , “MPEG digital audio coding”, IEEE signal processing magazine, Vol. 14, Issue 5, September 1997
[3] J. Herre, and Bernhard Grill, “Overview of MPEG-4 audio and its applications in mobile communications”, Proceeding of ICSP 2000
[4] M. Bosi, etc., “ISO/IEC MPEG-2 advanced audio coding”, J. AES Vol. 45, No. 10, 1997
[5] B. Grill, “MPEG-4 audio: A preview into the technology of the future”, 108th Convention of AES, February 2000.
[6] D. Schulz, “Improving audio codecs by noise substitution”, J. AES Vol. 44 No. 7/8 P. 593 ~ 598, 1996.
[7] E. Zwicker and H. Eberhard, “Psychoacoustics, facts, and models”, Berlin, Springer-Verlag, 1990
[8] Draft revision of recommendation ITU-R BS.1387, “Method for objective measurements of perceived audio quality”, 1998
[9] http://sound.media.mit.edu/mpeg4/audio/
[10] http://www.mp3-tech.org/
[11] J. G.beerends and J. A. Stemerdink, “A perceptual audio quality measure based on a psychoacoustic sound representation” J. AES Vol.40 No 12, December 1992
[12] A. Lerchs, “PEAQ software”, Version 0.1.3 alpha, http://www.mp3-tech.org/
[13] http://home.wanadoo.nl/~w.speek/eaqual.htm/
[14] ISO/IEC, JTCI/SC29/WG11 MPEG, “Information technology — Coding of audio-visual objects — Part 3: audio”, JTCI/SC29/WG11, Committee Draft 14996-3 1999

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