||Adaptive Dynamic Range Adjustment and Compensated Active Noise Cancellation for Amplification and Audiometric Tests Using Bluetooth Assistive Listening Devices
||Department of Electrical Engineering
assistive listening device (ALD)
Mandarin Hearing in Noise Test (MHINT)
adaptive dynamic range optimization (ADRO)
Bluetooth, Mandarin Monosyllable Recognition Test (MMRT)
active noise cancellation (ANC)
hearing threshold test
real-ear attenuation at threshold (REAT)
在聽力測試方面，本研究在安靜、45 dB HL遮蔽窄頻噪音、寬頻語音噪音與白噪音環境下比較信號補償式主動噪音消除耳機與TDH39、Audiocups等聽力測試耳機。24位年齡分佈於20–25歲的正常聽力個案參與此項研究。噪音環境下的閾值平移以純音閾值量測結果來計算；實耳降噪能力則以實耳閾值衰減(REAT)來界定。
助聽功能結果顯示，噪音環境下ADRO系統的MHINT語句聽辨值訊噪比在單耳配戴與未配戴間展現顯著性差異，但是線性裝置無顯著差異。整體語音音質滿意度顯示安靜環境下使用者對ADRO及線性系統同樣滿意，但是噪音環境下對ADRO比線性系統滿意。電話功能結果展現壓縮放大系統的MMRT平均語音聽辨得分顯著比線性裝置高(安靜及噪音環境下分別高出57% 及 53% )；語音音質滿意度指出安靜環境下使用者對兩種系統滿意度介於中度與滿意，然而噪音環境下對壓縮放大系統比線性裝置滿意。
聽力閾值測試結果發現在窄頻、寬頻語音與白噪音環境下，ANC耳機250及500 Hz的平均閾值顯著低於TDH39聽力測試耳機，250 Hz的平均閾值也顯著低於Audiocup聽力測試耳機；同時在窄頻噪音下，ANC耳機250及500 Hz的閾值平移與TDH39耳機相較分別減少14.2及12.3 dB。ANC耳機能夠在45 dB HL遮蔽寬頻語音與白噪音環境下以15 dB HL準確量測250 Hz的閾值，也能在窄頻噪音環境下以20 dB HL準確量測250 Hz的閾值，其結果和安靜環境並無區別，相對的TDH39 及Audiocups耳機則產生顯著的閾值平移。
以上結果展現自適性動態範圍調整應用於藍牙輔助聽力裝置助聽與電話功能對輕中度聽損個案的效益，特別是噪音環境下此效益更為顯著；在聽力閾值測試方面，信號補償式主動噪音消除耳機比傳統聽力測試耳機在250及500 Hz有較低的閾值平移，而且能夠在45 dB HL遮蔽窄頻與寬頻噪音環境下準確量測到20 dB HL閾值。此研究提出一藍牙輔助聽力裝置的創新架構設計，以自適性動態範圍調整應用於輔助聽力提升噪音下的訊噪比，同時以信號補償式主動噪音消除應用於噪音下閾值量測，此設計提供未來輔助聽力裝置搭配行動應用軟體執行輔助聽力與自我選配功能的方向。
Assistive listening devices (ALDs) are accessible and affordable solutions for helping people with hearing loss without the necessity of fittings by an audiologist. Traditional ALDs enhance the signal-to-noise ratio (SNR) by coupling signals at a long distance to a local device through wireless transmissions. Without a transmitter, the SNRs of body-worn devices that employ a linear amplification scheme are reduced significantly in noisy environments. Conversely, it is costly to integrate wireless technologies for accessing telephony and music functions in hearing aids that have superior performance to body-worn linear ALDs. This study incorporated the adaptive dynamic range adjustment and the compensated active noise cancelation (ANC) schemes into a Bluetooth ALD with amplification, telephony, music, and audiometric test functions. The benefits of these schemes in quiet and noisy environments were evaluated through comparison with linear schemes.
The adaptive dynamic range adjustment for assistive listening included adaptive dynamic range optimization (ADRO) in the amplification function and compression amplification in the telephony function, both of which were incorporated with a prescription for sloping-type sensorineural hearing loss. Comparisons were performed between linear and ADRO schemes in the amplification function, and between linear and compression amplification schemes in the telephony function in quiet and noisy environments. Seventeen and twelve native Mandarin speakers aged 21–68 years with mild to moderate sensorineural hearing loss participated in the studies of the amplification and telephony functions, respectively. The Mandarin Hearing in Noise Test (MHINT) and the Mandarin Monosyllable Recognition Test (MMRT) were the objective measurements for the amplification and telephony functions, respectively. Participant satisfaction was the subjective measurement for both functions.
In the audiometric tests, this study compared a custom-designed compensated hybrid ANC earphone with TDH39 and Audiocups audiometric earphones under conditions of quiet, 45 dB hearing level (HL) masking narrowband noise, wideband speech-shaped noise, and white noise. Twenty-four normal-hearing adults, aged 20–25 years, participated in this study. The pure-tone thresholds were measured to characterize the threshold shifts under noisy conditions, and real-ear attenuations at thresholds were assessed to quantify real-ear noise reduction performance.
For the amplification function, the ADRO system exhibited a significant difference in the MHINT reception threshold for sentences in noisy environments between monaurally aided and unaided conditions, whereas the linear system did not. The satisfaction rating regarding overall speech quality indicated that the participants were satisfied with the speech quality of both ADRO and linear schemes in quiet environments, and they were more satisfied with the ADRO scheme than with the linear scheme in noisy environments. Regarding the telephony function, the mean MMRT scores of the compression amplification scheme were significantly higher than those of the linear scheme (57% and 53% higher in quiet and noisy environments, respectively). The mean satisfaction ratings of both schemes were between neutral and satisfied in the quiet environment, whereas the participants were more satisfied with the compression scheme than with the linear scheme in the noisy environment.
Regarding the hearing threshold tests, the ANC earphone exhibited significantly lower mean thresholds than those of the TDH39 earphone at 250 and 500 Hz and those of the Audiocups earphone at 250 Hz under narrowband, speech-shaped, and white noise conditions. Compared with the TDH39 earphone at 250 and 500 Hz, applying a hybrid ANC earphone reduced threshold shifts by 14.2 and 12.3 dB, respectively, under the narrowband noise condition. Without a significant difference in performance from that under the quiet condition at 250 Hz, the ANC earphone was capable of measuring thresholds at a 15 dB HL presentation level under 45 dB HL masking speech-shaped and white noise conditions and a 20 dB HL presentation level under the narrowband noise condition, whereas the TDH39 and Audiocups earphones exhibited significant threshold shifts.
These results demonstrate the benefits of incorporating the adaptive dynamic range adjustment scheme with a prescription fitting for sloping-type hearing loss into the amplification and telephony functions of a Bluetooth ALD, especially in noisy environments, for people who experience mild or moderate hearing loss. In the hearing threshold tests, the compensated hybrid ANC earphone provided lower threshold shifts than the traditional audiometric earphones, and it was capable of measuring thresholds at 250 and 500 Hz with a presentation level starting from 20 dB HL under 45 dB HL masking narrowband and wideband noise. This paper provides an innovative design of a Bluetooth ALD in which the adaptive dynamic range adjustment scheme enhances SNRs for assistive listening and the compensated hybrid ANC enables threshold measurements in noisy environments. This study facilitates the development of assistive listening and self-fitting functions for future ALDs operated with mobile applications.
Table of Contents VII
Table Captions IX
Figure Captions X
Chapter 1 Introduction 1
1.1 Assistive Listening Devices 1
1.2 Amplification and Compression Strategies 4
1.3 Diagnosis of Hearing Loss 6
1.4 Organization of Dissertation 8
Chapter 2 Methods 10
2.1 Instruments 10
2.1.1 ALD 11
2.1.2 Compensated Active Noise Cancellation Earphone 11
2.2 Amplification and Compression Strategies for the Assistive Listening 13
2.2.1 Audiograms 13
2.2.2 Strategies for Amplification 13
2.2.3 Strategies for Telephony 17
2.3 Compensated Active Noise Cancellation Method for Hearing Tests 22
2.4 Participants 27
2.4.1 Participants for Amplification 28
2.4.2 Participants for Telephony 29
2.4.3 Participants for Hearing Tests 30
2.5 Data Collection 31
2.5.1 Data Collection for Amplification 31
2.5.2 Data Collection for Telephony 33
2.5.3 Data Collection for Hearing Tests 36
2.6 Statistical Analysis 38
Chapter 3 Results 39
3.1 Reception Threshold for Sentences and Satisfaction for Amplification 39
3.2 Word Recognition Scores and Satisfaction for Telephony 42
3.3 Hearing Test Results 44
3.3.1 Hearing Thresholds 44
3.3.2 Real-ear Attenuation at Thresholds 47
Chapter 4 Discussion 49
4.1 Amplification of ALD 49
4.2 Telephony of ALD 51
4.3 Hearing Tests 54
Chapter 5 Conclusion 58
Appendix A 67
Appendix B 68
Publication List 69
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