Adaptive Dynamic Range Adjustment and Compensated Active Noise Cancellation for Amplification and Audiometric Tests Using Bluetooth Assistive Listening Devices

  • 張 弘岳

Student thesis: Doctoral Thesis

Abstract

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
Date of Award2018 Feb 5
Original languageEnglish
SupervisorCheng-Chi Tai (Supervisor)

Cite this

Adaptive Dynamic Range Adjustment and Compensated Active Noise Cancellation for Amplification and Audiometric Tests Using Bluetooth Assistive Listening Devices
弘岳, 張. (Author). 2018 Feb 5

Student thesis: Doctoral Thesis