Clin Exp Otorhinolaryngol.  2018 Dec;11(4):267-274. 10.21053/ceo.2018.00052.

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

• Ahmadi R
• Jalilvand
• Mahdavi ME
• Ahmadi F
• Baghban AR

• KMID: 2439853
• DOI: http://doi.org/10.21053/ceo.2018.00052

Abstract

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.

Keyword

Directional Hearing Aid; Hearing Aids; Acceptable Noise Level; Hearing Loss; Digital Noise Reduction

MeSH Terms

Hearing Aids*
Hearing Loss
Hearing*
Humans
Noise*
Rehabilitation
Signal Processing, Computer-Assisted

Figure

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  Fig. 1. Real ear occluded gain (REOG) in dB, across frequencies (200–8,000 Hz) in opposite ear that is occluded by a tight ear impression. The original signal input (Digital Speech stimulus, average root mean of square of 65 dB sound pressure level [SPL]) and real ear occluded response (REOR) are shown in dB SPL. In order to obtain the REOG, the input signal level is subtracted from the REOR across frequencies. Values are presented as mean±standard deviation.

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  Fig. 2. Hearing thresholds for test ears. Values are presented as mean±standard deviation.

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  Fig. 3. Scatterplots showing the acceptable noise level (ANL) in dB for individual participants between two conditions. The comparisons are (A) omnidirectional-baseline and directional conditions, (B) omnidirectional-baseline and omnidirectional-broadband digital noise reduction (DNR) conditions, (C) omnidirectional-baseline and omnidirectional-multichannel DNR conditions, (D) directional and directional-multichannel DNR conditions, (E) directional and directional-broadband DNR conditions, and (F) directional-broadband DNR and directional-multichannel DNR conditions. Points above the diagonal line reflect better performance with hearing aid condition represented by the horizontal axis. Points below the diagonal line show better performance with the hearing aid condition represented by the vertical axis.

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  Fig. 4. The mean acceptable noise level (ANL) for the six digital noise reduction (DNR) and directionality conditions. There are statistically significant differences among the omnidirectional-baseline condition and omnidirectional-broadband DNR condition, directional condition, directional-broadband DNR condition, and directional-multichannel DNR condition. In addition, there are statistically significant differences among the omnidirectional-broadband DNR condition and directional condition, directional-broadband DNR condition, and directional-multichannel DNR condition. Also, there are statistically significant differences among the omnidirectional-multichannel DNR condition and directional condition, directional-broadband DNR condition, and directional-multichannel DNR condition. The asterisks show the statistical significant difference for each comparison.

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  Fig. 5. The acceptable noise level (ANL) benefit under five different directionality/digital noise reduction (DNR) conditions for all participants.

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