使用麥克風陣列改善遠距會議聲訊品質之研究

Abstract

近年來在視訊會議或遠距教學等場合中，以麥克風陣列擷取聲音訊 號的方式受到相 當大的重視。由於麥克風陣列具有指向性以及干擾和迴 音消除等優異的特性，使得其十 分適合於接收移動音源。在本論文中， 吾人將針對麥克風陣列如何擷取目標訊號及壓抑 干擾和迴音等問題，分 別提出各種演算法。首先，藉著一分區多重波束功率比較的演算 法，使 麥克風陣列能夠擷取並追蹤聲音訊號。當環境中存在強大干擾訊號或迴音 時，則 利用麥克風陣列適應性的特性，使用一改良式 Buckley 寬頻波束 合成器，以壓抑特定方 向之干擾源和非目標訊號的部份。經由數值模擬 以及實際資料的實驗，吾人證實了此一 陣列系統確實呈現了目標訊號增 強以及壓抑干擾訊號和迴音消除的能力。由於此套演算 法未來將應用於 即時處理之上，在考量數位訊號處器的運算速度下，將使波束合成器無 法使用過多的分接數，進而限制其效能。若是在即時處理時能更進一步提 高麥克風的品 質，以及增加數位訊號處理器的運算能力，則可提高麥克 風陣列系統的效能且可適用更 複雜的環境。 The use of microphone arrays for the acquisition of sound signals has received considerable attention in teleconferencing and distance education. A microphone array has the distinctive features of beam steering and interference suppression which make it suitable for mobile sound source pickup.In this thesis, we will concentrate on the performance of a microphone arrayin acquiring desired signals, suppressing interference and cancanceling echoin a teleconferencing environment. In particular, we will present suitablealgorithms for the above problems. In our setting, the microphone arraysacquires and keeps track of sound signals via a sectorized multi-beam powercomparison algorithm. In case that strong interference and echo exist, themicrophone array operates in an adaptive mode in which a modified Buckleytype broadband beamformer is employed to suppress fixed direction interferenceand unwanted echo components. Through a set of numerical simulations and realdata experiments, we demonstrate that the developed array system does indeedexhibit the desired signal enhancement, interference suppression and echocancellation capabilities. For real-time operations, the numerical power ofthe DSP board may limit the performance of the proposed algrithm. Thus furtherefforts should be directed toward improving the efficiency of the broadbandbeamformer.