聲學回授音(Acoustic Feedback)對於助聽器使用者是主要干擾聲音辨識的因素之一，本研究提出新的適應性回授消除 (Adaptive Feedback Cancellation, AFC) 演算法，可以因應回授音頻率的變化，自動改變有限帶寬(Band-Limited, 簡稱BL)的頻率範圍，避免回授音能量較小的頻率在預測回授音上的干擾，達到較好的回授音抑制效果，而且不會因為回授音路徑變化而無法消去;另外加入係數平滑法(Coefficients Smoothing)和增益控制(Gain Control)來增加預測回授音的效果以及預防發散的聲音影響聽者舒適度，經過模擬，當回授音路徑能量集中高頻，本研究提出之架構比一般形式的AFC效能在誤差上改善4.46dB，外加穩定增益(Added Stable Gain簡稱ASG)可增加5.11dB，而訊號回授比(Signal to feedback ratio, SFR)也多出3.48dB，而在低頻時也不會像過去被提出的有限帶寬AFC一樣失效，並能夠正常的消除回授音。

In this thesis, a band-limited (BL) adaptive feedback cancellation algorithm (AFC) is proposed, and the BL frequency can be adjusted automatically. The proposed algorithm overcomes the limitation of traditional BL-filter-X AFC (BL-FX-AFC) and it can efficiently accommodate itself to the changed environment. We use a sliding discrete cosine transform (DCT) to realize the transform-domain least mean square algorithm (LMS), and adopt coefficient smoothing scheme and gain control method to improve the performance of feedback cancellation. The results show that the proposed AFC is better than basic AFC by 4.46dB in misalignment, 5.11dB in ASG, and 3.48dB in SFR while the spectrum power of feedback path concentrates on high-frequency band. Not like BL-FX-AFC, it can still cancel feedback noise without being out of control while the spectrum power of feedback path concentrates on low-frequency band. Therefore, it is very suitable for future applications in the area of hearing aids.

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