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研究生：	謝羽豪 Hsieh, Yu-Hao
論文名稱：	脈衝響應函數估測與被動式時間反轉理論應用於雜訊抑制及訊號分離之效能評估 Performance Evaluation of Impulse Response Estimation Methods for Noise Reduction and Source Separation Using Passive Time Reversal
指導教授：	涂季平 Too, Gee-Pinn
學位類別：	博士 Doctor
系所名稱：	工學院 - 系統及船舶機電工程學系 Department of Systems and Naval Mechatronic Engineering
論文出版年：	2013
畢業學年度：	101
語文別：	英文
論文頁數：	88
中文關鍵詞：	時間反轉、適應性數位濾波器、脈衝響應、雜訊抑制、聲源分離
外文關鍵詞：	time reversal, adaptive digital filter, impulse response, noise reduction, source separation
相關次數：	點閱：112 下載：1
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雜訊抑制和聲源分離是聲訊處理的主要功效和目標，本研究主軸即根據時間反轉理論提出一套聲訊處理的流程，並由這兩項功效作為指標來對流程細節加以分析討論．由於時間反轉理論在應用時須使用收發陣列且聚焦效果會出現在原聲源處，造成在某些情況下無法適用，因此本研究選取適應性數位濾波器、最佳化解摺積流程、及相關函數等不同計算脈衝響應函數的方法，以脈衝響應函數作為聲波傳播路徑的模型，來克服上述時間反轉理論的使用限制．為了討論三種方法的適用性，在模擬部分設計了多種假設情境以評估探討諸如適用頻率範圍及抗雜訊能力等特性；在實驗部分，規劃在多種環境下進行，以評估選取方法的適當性，並驗證融合脈衝響應函數所設計出之時反處理流程對於提升訊雜比和還原各聲源訊號的功效．

根據模擬與實驗，本文結論採用訊雜比及相關係數作為評估優劣的指標，此外各方法所需的計算時間亦在討論範圍之內，因為關係到此時反流程對於發展成即時處理系統的可能性．分析結果顯示，所提出的時反聲訊處理流程確實具備提升訊雜比及還原聲源訊號這兩項目標功能，而不同的計算脈衝響應函數方法則展現了不同的優缺點，須視應用情況選用．當聲場內不具有明顯雜訊源，且計算時間為優先考量時，相關函數是建議的選項；如果重建訊號的完整性是關鍵目標且計算時間充裕，最佳化解摺積流程展現了良好的還原聲源效果；要是以抑制雜訊、從嘈雜環境中提取有效訊號為首要目標，則選取適應性數位濾波器最為合適．此外，適應性數位濾波器亦展現對於各種聲源訊號與環境邊界條件等的傑出可適性，且由於主動式噪音控制的先例而被視為極有潛力應用於即時聲源訊號處理系統的方法．

Noise reduction and signal separation are important functions of acoustic signal processing. This study presents a detailed analysis for designing an acoustic signal processing procedure based on the time reversal method. For some applications, setting transducers to retransmit at source locations or focusing at source location are impracticable. Modeling a wave propagation path between two points using impulse response function is one way to overcome this limitation. This thesis introduces alternative methods to calculate impulse response function including adaptive digital filter, optimal deconvolution process, and correlation. A discussion about applicability is provided on the applicable frequency range, anti-noise ability, and assumptive scenario interferences of the impulse response functions obtained by all three techniques through simulation, and subsequently applies them to the designed time reversal process to enhance the signal-to-noise ratio (SNR) and restore individual source signals through experimentation. These experiments are conducted with various environmental conditions to evaluate the suitability of selected methods for impulse response functions and verify the effects of proposed procedure.

The conclusions of this study are given based on the level of accuracy using the SNR and correlation coefficient as indicators, and the computation time required by alternative methods is also an important factor to be discussed for real-time system design. Results prove that the proposed passive time reversal process is capable of enhancing the SNR and restoring the source signal. The alternative methods of calculating the impulse response function offer various advantages, and should be selected according to the application. If the time-cost is the first consideration and there is no dominant noise source, then correlation is the best choice for calculating impulse response function. If completeness of the reconstructed signal is the key point, the optimal deconvolution process is appropriate. If noise reduction is the highest priority in extracting a useful signal from noisy environments while ensuring acceptable restoration capability and computation time, an adaptive digital filter is suitable. Besides, adaptive digital filter contains best applicability for various kinds of source waveforms and has great potential to be applied to a real-time procedure.

摘要 I
ABSTRACT III
ACKNOWLEDGEMENTS V
LIST OF TABLES IX
LIST OF FIGURES X
NOMENCLATURE XVI

I. INTRODUCTION 1
1.1 MOTIVATION AND OVERVIEW 1
1.2 LITERATURE REVIEW 3
1.3 THESIS ORGANIZATION 7
II. TIME REVERSAL AND ALTERNATIVE METHODS FOR IMPULSE RESPONSE FUNCTION 9
2.1 TIME REVERSAL AND PHASE CONJUGATION 9
2.2 PASSIVE TIME REVERSAL PROCEDURE 12
2.3 ADAPTIVE DIGITAL FILTER 14
2.4 OPTIMAL DECONVOLUTION PROCESS 17
2.5 CORRELATION FUNCTION 20
III. SIMULATIONS FOR EVALUATING THE APPLICABILITY OF SELECTED METHODS 22
3.1 FREQUENCY BANDWIDTH TEST 23
3.1.1 Single frequency sine wave 23
3.1.2 Chirp signal 25
3.1.3 Dirac delta function 27
3.2 ANTI-NOISE TEST 29
3.2.1 Non-coherent noise 29
3.2.2 Coherent noise 31
3.3 EXTRA FREQUENCY BANDWIDTH WITH DIFFERENT NOISE LEVEL TEST 33
3.4 MULTIPLE SOURCES INTERFERENCE TEST 38
3.5 COMPUTATION TIME COMPARISON 43
IV. EXPERIMENTS FOR COMPARING NOISE REDUCTION ABILITY, SIGNAL RECONSTRUCTION COMPLETENESS, AND SOURCE SEPARATION EFFECT 45
4.1 EXPERIMENTS IN A HALLWAY 46
4.1.1 Single source emitting chirp signal 49
4.1.2 Multiple sources emitting chirp signal and white noise 56
4.2 EXPERIMENTS IN A SEMI-ANECHOIC CHAMBER 61
4.2.1 Evaluating the suitability of introduced methods using music, woman voice, and man voice (transmitted in sequence) 62
4.2.2 Analysis and comparison according to SNR and cross-correlation coefficient when sources emit simultaneously 70
4.3 EXPERIMENTS IN A CONFERENCE ROOM 74
4.3.1 Applying adaptive digital filter to calculate impulse response functions (sources transmitted in sequence) 75
4.3.2 Analysis and comparison according to SNR and cross-correlation coefficient when sources emit simultaneously 78
V. CONCLUSIONS 82
VI. FUTURE WORKS 85

REFERENCES 86
                                    

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校內：2014-08-01公開
校外：2014-08-01公開

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