臺灣博碩士論文加值系統

以小波分頻的訊號壓縮技術已被廣泛地應用在音視訊編碼系統中，而漸進式零樹編碼方法(Embedded Zero-Tree Coding)更被證實可成功地運用在靜態影像壓縮上；本論文以研究樂音(Audio)的壓縮編碼方法為主，提出M-EZWP (Masking-Embedded Zero-tree Wavelet Packet)系統，以小波封包(Wavelet Packet)分頻方式，將樂音訊號經由濾波器群組分成29個次頻帶，其頻寬分布與人類聽覺的26個關鍵頻帶(Critical Band)相近，藉以找出人耳聲學模型(Psychoacoustic Model)中的最小遮蔽臨界值(Minimum Masking Threshold)，此值將輸入零樹編碼方塊中，藉由零樹編碼將每個次頻帶的係數依照其重要性程度予以編碼傳送，可大幅降低位元率，並由於其擁有漸進式傳輸(Embedded)的特性，可依通道的狀況及不同的品質需求達成可變位元率(variable bitrate)的傳送，CD品質單聲道樂音位元率可達40Kbps，解碼後的樂音品質與MPEG audio Layer II相比，可達到聽覺上更好的效果。

The wavelet filter bank analysis-synthesis technique has been popularly applied in many areas of digital signal processing, including audio and video coding. The embedded zero-tree wavelet (EZW) coding has shown great performance in progressive image coding. In this work, we focus on high quality audio coding which delivers transparent perceptual quality. The segmented audio signal is divided into 29 subbands via wavelet packet analysis, and then coded by a zero-tree coder with the modified algorithm based on the minimum masking thresholds which are generated by the psychoacoustic model. Subjective listening tests show that the Masking-Embedded Zero-tree Wavelet Packet (M-EZWP) system we propose has better performance compared with MPEG audio Layer II standard, especially in the case of very low bitrate. The perceptual transparent quality of monophonic audio can be achieved at about 40 Kbps. Furthermore, the M-EZWP system could be adjusted to various network conditions, such as VBR and CBR transmissions because of the embedded property.

摘要I
AbstractII
目錄III
圖目V
表目VII
第一章 緒論 1
1.1音訊壓縮簡介1
1.2研究動機與目的3
1.3系統架構 4
1.4論文架構 5
第二章 小波簡介 6
2.1 小波轉換(wavelet transform) 6
2.1.1小波分解(wavelet expansion)與離散小波轉換 6
2.1.2多重解析度（Multiresolution）分析 7
2.2小波濾波器 9
2.3小波封包(wavelet packet) 16
2.4延遲問題處理 17
2.5系統分頻架構 19
第三章 人耳聲學模型 24
3.1基本原理與其應用 24
3.1.1雜訊對單頻音的遮蔽效應 26
3.1.2頻音對單頻音的遮蔽效應 29
3.1.3時間軸上的遮蔽效應 31
3.2 模型公式 32
3.3訊號之各頻帶的最小遮蔽臨界值 35
第四章 漸進式零樹(Zero-Tree)編碼系統39
4.1 零樹編碼之樹狀結構39
4.2 零樹搜尋法則 44
4.3 漸進式與交錯式的碼傳送方式49
4.4 連續近似量化(SAQ) 50
第五章 實驗結果及討論 55
5.1 樂音壓縮位元率 55
5.2 樂音壓縮零樹之樹狀架構評估 58
5.3 樂音壓縮品質評估 59
5.3.1經由小波分頻合成後的樂音品質 60
5.3.2經由系統編碼解碼後的樂音品質 61
5.4 系統複雜度評估 63
第六章 結論 65
參考文獻 66

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