The Effect of Digital Noise Reduction on Annoyance and Speech Perception in Low and High Acceptable Noise Level Groups

THIEME Original Research The Effect of Digital Noise Reduction on Annoyance and Speech Perception in Low and High Acceptable Noise Level Groups Hemanth Narayan Shetty1 Navya Bilijagalemole Nanjundaswamy1 1 Department of Audiology, All India Institute of Speech and Hearing Mysuru, Mysore, Karnataka India Int Arch Otorhinolaryngol 2019;23:433–439. Abstract Keywords ► noise reduction ► hearing aid ► annoyance ► speech perception Introduction Studies have reported that although speech perception in noise was unaltered with and without digital noise reduction (DNR), the annoyance toward noise measured by acceptable noise level (ANL) was significantly improved by DNR with the range between 2.5 and 4.5 dB. It is unclear whether a similar improvement would be observed in those individuals who have an ANL  14 dB (predictive of poor hearing aid user) often rejects their aid because of annoyance toward noise. Objectives (a) To determine the effect of activation of DNR on the improvement in the aided ANL from low- and high-ANL groups; and (b) to predict the change in ANL when DNR was activated. Method Ten bilateral mild to severe sloping sensorineural hearing loss (SNHL) participants in each of the low- and high-ANL groups were involved. These participants were bilaterally fitted with receiver in canal (RIC) hearing aids (Oticon, Smorum, Egedal, Denmark) with a DNR processor. Both SNR-50% (Signal to noise ratio (in dB) required to achieve 50 % speech recognition) and ANL were assessed in DNR-on and DNR-off listening conditions. Results Digital noise reduction has no effect on SNR-50 in each group. The annoyance level was significantly reduced in the DNR-on than DNR-off condition in the low-ANL group. In the high-ANL group, a strong negative correlation was observed between the ANL in DNR off and a change in ANL after DNR was employed in the hearing aid (benefit). The benefit of DNR on annoyance can be effectively predicted by baselineaided ANL by linear regression. Conclusion Digital noise reduction reduced the annoyance level in the high-ANL group, and the amount of improvement was related to the baseline-aided ANL value. Introduction Individuals with cochlear hearing loss frequently complain of difficulties in following speech in noisy conditions.1 Kochkin2 reported that
62.3% of these individuals are dissatisfied with hearing aids, out of which 25.3% reject their hearing aid because of background noise. To overcome this problem, hearing aid manufacturers have implemented noise reduction received December 21, 2018 accepted April 1, 2019 Address for correspondence Hemanth Shetty, PhD, Department of audiology, All India Institute of Speech and Hearing Mysuru, Manasagongothri, Mysore, Karnataka, 570006, India (e-mail: ). DOI https://doi.org/ 10.1055/s-0039-1688811. ISSN 1809-9777. algorithms in the hearing aid circuitry.3 The noise reduction algorithm analyses the speech (higher modulation depth) from noise (low modulation depth) through identification of the inherent modulation depth. If the speech and noise shares the same frequency band then a gain reduce at the frequency corresponds to noise band. Bentler et al4 reviewed laboratory studies of digital noise reduction (DNR), and her findings showed an equivocal response on the subjective benefit of Copyright © 2019 by Thieme Revinter Publicações Ltda, Rio de Janeiro, Brazil 433 434 The Effect of Digital Noise Reduction on Annoyance and Speech Perception DNR in the real world. However, improvement in speech perception5 and a significant reduction in the annoyance level were evident when DNR was active.6–8 A reliable clinical measure to document annoyance from a background noise is the acceptable noise level (ANL).9 Acceptable noise level is a measure of the willingness to accept background noise while listening to speech.10 The ANL is calculated by taking the difference between the most comfortable level (MCL) for running speech and the maximum background noise level (BNL) that a listener is willing to accept. The ANL ranges between - 3.5 and 27 dB.11 ANLs could predict a listener’s success of hearing aids with 85% accuracy.12 It was found that ANL was significantly improved by 4.2 dB on average when DNR was activated,13 which is circumscribed to the ANL range (- 3 to 14 dB) of the participants of the present study. It is pertinent to determine how much reduction in ANL can be observed when DNR is active in low- ( 7 dB) and high-ANL ( 13 dB) groups, which cannot be inferred from the study of Mueller et al.13 This is important because the high-ANL group is the one who often rejects their hearing aid, since they are less able to put up with background noise while listening to speech.14 In addition, a clinician can objectively counsel a patient on the amount of noise above which they would be showing annoyance and its improvement after the activation of DNR in the hearing aid. Further, it helps a client to consider in procuring a hearing aid that has the option of DNR, so that rejection can be minimized. Thus, it is relevant to quantify the change in ANL on hearing impaired individual, when DNR is active. The objective of DNR algorithms is to decrease a gain in the frequency regions corresponding to the background noise, which reduces annoyance from background noise and increases the potential of understanding speech in the presence of noise. Thus, it is hypothesized that the effect of DNR may bring out dramatic changes in the annoyance level, especially in individuals who are able to put up with less noise. The following research question is framed: how does the DNR influence the annoyance level and speech perception in the presence of noise in low- and high-ANL groups? The specific objective was designed to determine if the activation of DNR would improve the aided ANL of low- and high-ANL groups. In addition, we sought to predict the change in ANL, if any, when DNR was activated. Shetty et al. Material and Methods Participant Inclusion Criteria A single blinded simple randomized one-shot postcomparative research design with repeated measures was used to investigate the effect of DNR on annoyance and on speech perception in low- and high-ANL groups. A convenient sampling method was used to select the participants. A total of 20 participants within an age range between  60 to  75 years old who had acquired bilateral mild to severe sloping sensorineural hearing loss (SNHL) were involved. The participants were grouped into low- (n ¼ 10; mean ANL ¼ 5.5 dB; ANL range: 3–7 dB) and high-ANL (n ¼ 10; mean ANL ¼ 18.41 dB; ANL range: 3–7 dB) based on the scores of the ANL test. The data of the aided ANL and speech perception in the presence of noise were measured from every participant of each group in DNR-activated and DNR-deactivated conditions. The conditions were randomized across the participants. All of the participants had normal middle ear status, as indicated by ‘A’ type tympanogram. The participants were native speak (...truncated)