本論文提供一能提昇語音辨識率的麥克風陣列。利用指向性比一般陣列高的超指向性麥克風陣列（其為端射陣列,endfire array），能夠達到減噪的效果，特別是當噪音在陣列背後的時候。評估表現的客觀參數有三種：指向性因子（directivity index）、前後比（front-to-back ratio）以及不變的波束寬（constant beam-width），利用將上述三種客觀參數最佳化，便能得到設計出超指向性麥克風陣列的濾波器。另一方面，如果噪音並不是在陣列背後的方向，相反地，是在靠近語音訊號的位置，則需使用另一種稱之為相位差評估（phase difference estimation）的演算法來解決這種問題，此方法能在不使語音訊號失真的情況下消除噪音。本研究發現在相位差評估內的ITD threshold 對於語音辨識提昇的效果扮演著重要的角色，因此必須要將其作一最佳化的設計，在此本研究是使用GSS（Golden Section Search）來將其最佳化。此外，音量亦會影響辨識率，因此
也必須要加以控制。如果目標訊號並不是在設計的主軸上，則必須要使用beam-steering 的技術將主波束轉置目標訊號的位置上。最後將會分析實驗結果，並驗證本研究所提出之演算法能夠使語音辨識率大幅提昇。

摘 要 i
ABSTRACT ii
誌謝 iii
TABLE OF CONTENTS iv
LIST OF TABLES vi
LIST OF FIGURES vii
I. INTRODUCTION 1
II. SUPER-DIRECTIVE MICROPHONE ARRAYS 4
A. First-order difference microphone array 4
1. First order adaptive DMA 6
B. Optimization of array beampattern 8
1. Maximum for directive index (MDI) 8
2. Maximum for front-to-back ratio (MFBR) 9
3. Maximum for constant beamwidth (MCBW) 10
C. Super-directive microphone array with equalizer 11
D. Simulated and experimental results 12
III. PHASE-DIFFERENCE ESTIMATION (PDE) 13
v
A. Optimization of the ITD threshold using GSS 14
1. Golden section search 15
2. The Optimal ITD threshold varying with the included angle 16
B. Volume scaling 18
C. Beam steering 18
D. Simulated and experimental results 19
IV. CONCLUSIONS 22
REFERENCES 23

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