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標題: 應用可變步階的方法於主動噪音控制系統中的線上回授路徑建模
Using Variable Step Size Method for OnlineFeedback Path Modeling in Active Noise ControlSystems
作者: Shen, Jian-Hung
關鍵字: active noise control;主動噪音控制;acoustic feedback;variable step size;聲音回授;可變步階
出版社: 機械工程學系所
雙麥克風架構的主動噪音控制系統是由參考麥克風與誤差麥克風所組成。因為參考麥克風不僅會量測到噪音的部分,也擷取到控制喇叭回傳的訊號,所以引發了聲音回授的問題。傳統演算法並未進行聲音回授補償,使控制器權重的更新受到了影響。現有處理聲音回授問題的方法中,主要是加入兩個適應性濾波器於傳統的演算法中,分別作為鑑別器與輔助鑑別器,進行線上回授路徑建模以及提升系統的收斂性,以便估算出聲音回授訊號的大小,進而對參考麥克風量測到的訊號進行聲音回授補償。但傳統演算法中存在置換誤差的問題,而降低系統的消音性能。因此本篇於文獻方法中加入置換誤差與可變式正規化step size的觀念,以便有較好的收斂速度與消音性能,提出了vss-CNFxLMS/CE-AF演算法。本文透過一維聲管的架構實現所提出的演算法進行實驗。由實驗的方式進行可變式step size的參數分析,歸納出參數選取的頃向。從實驗結果驗證應用此演算法的主動噪音控制系統,能夠有效降低聲音回授對系統的影響,並有良好的消音性能。

Active noise control (ANC) system of a two-microphone structure has a reference microphone and an error microphone. The reference microphone will pick up a signal from the feedback path of the ANC system, causing the acoustic feedback problem. An approach using three adaptive filters from the literature is thus adopted in this study to overcome the problem. One adaptive filter is used as identifier to model the feedback path on-line, another is used as auxiliary identifier to improve the identification accuracy of the identifier, and the other is as controller to compute control signal. From the identifier, an estimate of the acoustic feedback signal can be obtained and used to compensate the signal from reference microphone so that compensated signal can have a better correlation to the primary noise. The compensated signal is then used to the controller such that a desired ANC performance can be achieved. Nevertheless, ANC performance of the approach is limited due to usage of constant step sizes in a combined adaptive algorithm and lack of consideration of commutation error (CE). In order to obtain a better ANC performance, a new combined algorithm named as vss-CNFxLMS/CE-AF algorithm that includes CE and variable step sizes into the adopted approach is thus proposed in this study. A one-dimensional acoustic duct system is further setup for ANC experiments to evaluate the proposed algorithm. Experimental results demonstrate that the vss-CNFxLMS/CE-AF algorithm can effectively reduce the influence of the acoustic feedback in the ANC system and achieve a better performance.
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