本論文主要是以頻率域為基礎來設計迴聲消除器，有別於時間域迴聲消除器，頻率域迴聲消除器是以一段訊號為單位，然而時間域迴聲消除器是以單一訊號為單位，時間域迴聲消除器最大缺點是其中央處理器的負載量會很大，甚至在即時處理上會有很大的困難。但是頻率域迴聲消除器卻可以使中央處理器的負載量降低，非但在即時處理上可輕易的實現，還可以在同一段訊號內做數次疊代處理來提升回升消除之效果，此作法在本文稱為頻率域疊代比例正規化最小平方法。疊代過程中，可以依據輸入訊號能量大小調整疊代更新速率以同時達到準確模擬環境頻率響應以及使輸出迴聲訊號降至最低。至於雙方通話的條件下，在此會設計雙方通話偵測器，如果偵測到只有遠方在通話的條件下，模擬環境響應參數會不斷更新；然而當雙方通話偵測器偵測倒是雙方通話條件下，模擬環境響應參數會停止更新以防止參數發散。在單一頻道做迴聲消除其效果會有極限，然而在多頻道做迴聲消除卻可以提升效果，換句話說，利用麥克風陣列處理迴聲消除會比單頻道迴聲消除效果會更好，先是在多頻道輸入訊號加入波型束成器，使之變成單頻道訊號，此單頻道訊號可以只保留在收音範圍內訊號而阻隔在收音範圍外訊號，進而做迴聲消除，此方法達到雙重消除迴聲效果。更進階方法是在波型束成器設計成可適應性的，並且與單頻道迴聲消除融為一體，此方法可以更有效消除回升且對於各種不同迴聲訊號皆可以很有效的消除。利用加強回升消除率來判斷演算法對於迴聲消除表現好壞得知，麥克風陣列基底迴聲消除器比起單頻道迴聲消除器還要好上10 dB，最好的演算法甚至可高達約50dB。本文最後利用現成音檔輸入訊號比較頻率域各個迴聲消除方法以及利用單頻道迴聲消除法實現於及時訊號處理上。

This thesis presents acoustic echo cancellation (AEC) algorithms designed in the frequency-domain. Least-mean-square (LMS) based method, such as Proportionate Normalized LMS (PNLMS) method, is used to model the echo path and to match the desired signal at the near end. To enhance cancellation performance of the frequency-domain algorithms, internal iterations and are employed with the coefficient update loop. In addition, microphone array beamforming, such as Delay and Sum (DAS) Fixed Beamformer (FBF) method, Minimum Variance Distortionless Response (MVDR) FBF method and Generalized Sidelobe Canceller (GSC) method, is utilized to receive local speech signals while suppressing echo and interference at undesired directions. Double-talk detector (DTD) is developed to ensure the robustness of the AEC in double-talk scenarios. The proposed AEC algorithm integrated with DTD and the beamformer is validated with simulations and experiments. For single talk AEC performance, the Echo-Return Loss Enhancement (ERLE) for LMS method is 10 dB, for iterative PNLMS method is 35 dB and for GSC method is 50 dB, which is the best method in all AEC algorithms.

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