The Effects of Hearing Aid Digital Noise Reduction and Directionality on Acceptable Noise Level

Clinical and Experimental Otorhinolaryngology Vol. 11, No. 4: 267-274, December 2018 https://doi.org/10.21053/ceo.2018.00052 pISSN 1976-8710 eISSN 2005-0720 Original Article The Effects of Hearing Aid Digital Noise Reduction and Directionality on Acceptable Noise Level Roghayeh Ahmadi1·Hamid Jalilvand1·Mohammad Ebrahim Mahdavi1·Fatemeh Ahmadi2·Ali Reza Akbarzade Baghban1 Department of Audiology, School of Rehabilitation, Shahid Beheshti University of Medical Sciences, Tehran; 1 School of Economic, Allameh Tabataba’i University, Tehran, Iran 2 Objectives. Two main digital signal processing technologies inside the modern hearing aid to provide the best conditions for hearing aid users are directionality (DIR) and digital noise reduction (DNR) algorithms. There are various possible settings for these algorithms. The present study evaluates the effects of various DIR and DNR conditions (both separately and in combination) on listening comfort among hearing aid users. Methods. In 18 participants who received hearing aid fitting services from the Rehabilitation School of Shahid Beheshti University of Medical Sciences regularly, we applied acceptable noise level (ANL) as our subjective measure of listening comfort. We evaluated both of these under six different hearing aid conditions: omnidirectional-baseline, omnidirectional-broadband DNR, omnidirectional-multichannel DNR, directional, directional-broadband DNR, and directional-multichannel DNR. Results. The ANL results ranged from −3 dB to 14 dB in all conditions. The results show, among all conditions, both the omnidirectional-baseline condition and the omnidirectional-broadband DNR condition are the worst conditions for listening in noise. The DIR always reduces the amount of noise that patients received during testing. The DNR algorithm does not improve listening in noise significantly when compared with the DIR algorithms. Although both DNR and DIR algorithms yielded a lower ANL, the DIR algorithm was more effective than the DNR. Conclusion. The DIR and DNR technologies provide listening comfort in the presence of noise. Thus, user benefit depends on how the digital signal processing settings inside the hearing aid are adjusted. Keywords. Directional Hearing Aid; Hearing Aids; Acceptable Noise Level; Hearing Loss; Digital Noise Reduction INTRODUCTION intelligibility in babble noise, which cannot be improved while using a hearing aid [1,2]. For listening comfort and speech intelligibility in noise, there are two main digital signal processing (DSP) technologies, the digital noise reduction (DNR) and directionality (DIR), which are used when fitting current modern digital hearing aids. The DNR approach, which separates sounds based on their frequency and reduces the hearing aid gain into frequency bands with lower signal-to-noise ratios (SNRs), provides listening comfort in noise. It has been shown DNR reduces adverse effects of noise on memory for speech, helps the hearing aid user in noisy conditions, and prevents cognitive load during auditory processing [3,4]. On the other hand, DIR, which separates sounds based on a spatial approach, focuses on a specific direction (most commonly, in front), receives a target signal (speech) the hearing aid user probably prefers to hear (i.e., a tar- The role of the auditory system is detection, discrimination, and identification of various sounds and noises. The main function of this system for human beings is speech perception, known as speech intelligibility, especially in difficult auditory conditions, such as when there is noise. One of the main complaints of patients with sensory neural hearing loss is the problem of speech ••Received January 14, 2018 Revised March 10, 2018 Accepted April 17, 2018 ••Corresponding author: Hamid Jalilvand Department of Audiology, School of Rehabilitation, Shahid Beheshti University of Medical Sciences, Damavand St., Tehran, Iran Tel: +98-21-7756-1721, Fax: +98-21-7759-1807 E-mail: Copyright © 2018 by Korean Society of Otorhinolaryngology-Head and Neck Surgery. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 267 Vol. 11, No. 4: 267-274, December 2018 get speech in a group), and improves the SNR of the listening environment [5]. These two algorithms inside a digital hearing aid work together to provide optimal amplification coupled with the highest possible speech intelligibility in noise. Although it has been demonstrated DNR algorithms provide an improvement in subjective measurements [6,7], few studies show the objective improvement provided by DNR [8]. Typically, in some specific hearing aids, the DNR algorithm can be fitted as two main types: broadband DNR and multichannel DNR. The former algorithm involves gain reduction by a default amount through a whole range of hearing aid gain frequency responses when the hearing aid detects noise. Under this condition, the gain is decreased proportionally in the overall frequency range (Supplementary Table 1, Supplementary Figs. 1-5). The latter algorithm involves a specific amount of gain reduction that is both determined and limited by the audiologist during the hearing aid fitting. In a multichannel DNR, by applying various settings, there could be different DNR conditions. In clinical practice, there are no generally accepted rationale for selecting comparable DNR algorithms and settings when fitting modern hearing aids [9]. Practically, they are adjusted in terms of the audiologist’s experience and are based on clinical trial protocols or specific procedures recommended by hearing aid companies. Also, there has been no study to both compare broadband DNR with multichannel DNR and the various conditions of multichannel DNR. In this study, we used the acceptable noise level (ANL) as our measurement of subjective comfort [10]. We compared both the effectiveness of DIR and two different DNR settings (broadband vs. multichannel DNR) separately. In addition, we compared the efficacy of both algorithms (DNR and DIR) by measuring the ANL. The ANL was chosen because it has been shown the ANL can prove the effectiveness of noise reduction is provided by DNR algorithms [8,11]. Our main purpose is to evaluate the effectiveness of DIR and DNR technologies (both alone and in combination) on patient performance in noise. H I G H L I G H T S Among all conditions, both the omnidirectional-baseline condition and the omnidirectional-broadband digital noise reduction (DNR) condition are the worst conditions for listening in noise. The directionality (DIR) always reduces the amount of noise that patients received during testing. The DNR algorithm does not improve listening in noise significantly when compared with the DIR algorithms. Although i (...truncated)