臺灣博碩士論文加值系統

回饋音是讓助聽器使用者經常常抱怨的一個問題，而回饋音與閉塞效應對於助聽器的設計與使用是一大挑戰。然而較早期為了同時能解決回饋音與閉塞效應常常陷入兩難的局面，此研究中分別討論消除回饋音的幾種策略同時降低閉塞感。
現今發展出主要消除回饋音的策略分別有主動式調變增益值(Gain reduction)、陷波濾波器(Notch filter)、相位消除法(Phase cancellation)這三種，其中主動式調變增益值會限制住了助聽器整體的最大使用增益上限，而陷波濾波器又會造成訊號的遺漏，所以各有其缺失，相對的相位消除法不僅能夠在不調低增益的情況下抑制回饋音，更能夠保留住原始訊號之完整性，所以本研究主要目的為使用 NLMS(Normalized Least Mean Squares)相位消除演算法進行助聽器回饋音消除並將此演算法實現於GA3280 晶片中。依據所設計實驗去驗證當回饋音消除功能開啟(即將NLMS演算法實現後)，在標準聽力室環境中，重要頻帶下可提升約10dB的最大穩定增益量。而且能夠完整的保留住原始訊號之特性。

Feedback is one of the most frequent complaints of hearing aid users. Feedback and the occlusion effect pose great challenges for hearing aid design and usage. However, conventional solutions for those two problems often face the dilemma. In this research will discuss some advanced signal processing strategies of the feedback cancellation and the occlusion effect reduction.
The strategies currently used to reduce feedback (i.e.,adaptive feedback reduction algorithms using adaptive gain reduction, notch filtering, and phase cancellation strategies). The adaptive gain reduction will limit the allowable maximum gain, and notch filtering may cause some signal loss, there are different defects will occurred. But the phase cancellation strategy not only can limit the allowable maximum gain, but also keep the signal’s completeness. This research main purpose is to use the phase cancellation strategy by NLMS(Normalized Least Mean Squares) algorithm to cancel the feedback noise by digital processor chip (GA-3280) in hearing aid. According to the experiment in our design when feedback cancellation starting. In standard sound booth would increase 10 dB SPL of allowable maximum gain and can keep the signal’s completeness.

目錄
致謝 I
摘要 II
Abstract III
目錄 IV
圖目錄 VI
表目錄 VIII
第一章 緒論 1
1.1 前言 1
1.2 研究動機與目的 2
1.3 論文架構 3
第二章 文獻回顧與相關原理介紹 5
2.1 使用者需求度 5
2.2 聲學回饋路徑 6
2.3 助聽器聲學回饋路徑與其影響 6
2.3.1 助聽器聲學回路徑 6
2.3.2 助聽器回饋音相關因素 7
2.3.3 助聽器回饋音之影響 8
2.4 助聽器回饋音消除策略 9
2.4.1 主動式調變增益值 10
2.4.2 陷波濾波器 11
2.4.3 相位消除法 11
2.5 相位消除演算法介紹 13
2.5.1 LMS(Least Mean Squares) 14
2.5.2 NLMS(Normalized Least Mean Squares) 18
第三章 研究流程架構與設計方法 20
3.1 軟硬體設備介紹 21
3.2 回饋音消除功能驗證配置 22
3.3 助聽器訊號處理流程 23
3.4 雛形助聽器架構設計 24
3.4.1 GA-3280 數位訊號處理晶片介紹 24
3.4.2 GA-3280 發展板介紹 26
3.5 助聽器相位消除演算法系統架構圖 27
3.6 助聽器晶片與電腦平台溝通介面 28
3.7 助聽器機構設計與組裝 29
3.7.1 助聽器麥克風之聲電特性 30
3.7.2 助聽器喇叭之聲電特性 31
第四章 實驗結果分析與討論 33
4.1 相位消除法NLMS驗證 33
4.1.1 發展板上模擬之結果 33
4.1.2 實體助聽器於聲電分析儀測試 35
4.2 改變延遲時間測試NLMS演算法之效益 38
4.3 最大穩定增益(Add Stable Gain)測試與驗證 43
4.3.1 比較GA-3280助聽器與Phonak-Savia助聽器 44
4.4 驗證NLMS消除演算法下之訊號完整性 46
4.5 分析比較LMS與NLMS演算法 48
第五章 結論與未來展望 51
參考文獻 53

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