Effectiveness of directional microphones and noise reduction schemes in hearing aids: a systematic review of the evidence.

Department of Speech Pathology and Audiology, University of Iowa, Iowa City 52242, USA.
Journal of the American Academy of Audiology (Impact Factor: 1.59). 06/2005; 16(7):473-84. DOI: 10.3766/jaaa.16.7.7
Source: PubMed

ABSTRACT A systematic review of the literature was undertaken to find evidence of real-world effectiveness of directional microphone and digital noise reduction features in current hearing aids. The evidence was drawn from randomized controlled trials, nonrandomized intervention studies, and descriptive studies. The quality of each study was evaluated for factors such as blinding, power of statistical analyses, and use of psychometrically strong outcome measures. Weaknesses in the identified studies included small sample size, resultant poor power to detect potentially worthwhile differences, and overlapping experimental conditions. Nine studies were identified for directional microphones, and the evidence (albeit weak) supports effectiveness. Two studies were identified for the noise reduction feature, and the evidence was equivocal. For the researcher, such a systematic review should encourage the careful consideration of appropriate methodologies for assessing feature effectiveness. For the clinician, the outcomes reported herein should encourage use of such a systematic review to drive clinical practice.

Download full-text


Available from: Ruth Bentler, Feb 28, 2015
  • Source
    • "Modern hearing aids often incorporate directional microphones that can provide a substantial signal-to-noise ratio (SNR) improvement—and typically a corresponding speech-intelligibility benefit—over omnidirectional microphones (Bentler 2005). To obtain the maximal benefit, however, requires an ideal set of conditions (Valente et al. 1995): the listening environment should have no more than moderate reverberation (i.e., the level of the direct and reflected sound should be at least equal), the background noise should be at the side or the rear of the listener, and the listener should be more or less facing the signal of interest (Ricketts & Dhar 1999; Hornsby & Ricketts 2007). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Although directional microphones on a hearing aid provide a signal-to-noise ratio benefit in a noisy background, the amount of benefit is dependent on how close the signal of interest is to the front of the user. It is assumed that when the signal of interest is off-axis, users can reorient themselves to the signal to make use of the directional microphones to improve signal-to-noise ratio. The present study tested this assumption by measuring the head-orienting behavior of bilaterally fit hearing-impaired individuals with their microphones set to omnidirectional and directional modes. The authors hypothesized that listeners using directional microphones would have greater difficulty in rapidly and accurately orienting to off-axis signals than they would when using omnidirectional microphones.
    Ear and Hearing 09/2014; 35(5):e204-e212. DOI:10.1097/AUD.0000000000000053 · 2.83 Impact Factor
  • Source
    • "For example, most hearing aids have some type of proprietary digital noise-reduction (DNR) algorithm that utilizes a slow-acting, modulation-based strategy and/ or a fast-acting filtering strategy (Bentler, 2005; Mueller and Ricketts, 2005; Bentler and Chiou, 2006). These technologies all share the general goal of reducing the level of signals identified as noise or other unwanted signal distortions. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Transient noise can be disruptive for people wearing hearing aids. Ideally, the transient noise should be detected and controlled by the signal processor without disrupting speech and other intended input signals. A technology for detecting and controlling transient noises in hearing aids was evaluated in this study. The purpose of this study was to evaluate the effectiveness of a transient noise reduction strategy on various transient noises and to determine whether the strategy has a negative impact on sound quality of intended speech inputs. This was a quasi-experimental study. The study involved 24 hearing aid users. Each participant was asked to rate the parameters of speech clarity, transient noise loudness, and overall impression for speech stimuli under the algorithm-on and algorithm-off conditions. During the evaluation, three types of stimuli were used: transient noises, speech, and background noises. The transient noises included "knife on a ceramic board," "mug on a tabletop," "office door slamming," "car door slamming," and "pen tapping on countertop." The speech sentences used for the test were presented by a male speaker in Mandarin. The background noises included "party noise" and "traffic noise." All of these sounds were combined into five listening situations: (1) speech only, (2) transient noise only, (3) speech and transient noise, (4) background noise and transient noise, and (5) speech and background noise and transient noise. There was no significant difference on the ratings of speech clarity between the algorithm-on and algorithm-off (t-test, p = 0.103). Further analysis revealed that speech clarity was significant better at 70 dB SLP than 55 dB SPL (p < 0.001). For transient noise loudness: under the algorithm-off condition, the percentages of subjects rating the transient noise to be somewhat soft, appropriate, somewhat loud, and too loud were 0.2, 47.1, 29.6, and 23.1%, respectively. The corresponding percentages under the algorithm-on were 3.0, 72.6, 22.9, and 1.4%, respectively. A significant difference on the ratings of the transient noise loudness was found between the algorithm-on and algorithm-off (t-test, p < 0.001). For overall impression for speech stimuli: under the algorithm-off condition, the percentage of subjects rating the algorithm to be not helpful at all, somewhat helpful, helpful, and very helpful for speech stimuli were 36.5, 20.8, 33.9, and 8.9%, respectively. Under the algorithm-on condition, the corresponding percentages were 35.0, 19.3, 30.7, and 15.0%, respectively. Statistical analysis revealed there was a significant difference on the ratings of overall impression on speech stimuli. The ratings under the algorithm-on condition were significantly more helpful for speech understanding than the ratings under algorithm-off (t-test, p < 0.001). The transient noise reduction strategy appropriately controlled the loudness for most of the transient noises and did not affect the sound quality, which could be beneficial to hearing aid wearers.
    Journal of the American Academy of Audiology 09/2012; 23(8):606-15. DOI:10.3766/jaaa.23.8.4 · 1.59 Impact Factor
  • Source
    • "The benefits of directional microphones for improving speech understanding in noise for adults who use HAs have been previously documented in three systematic reviews (Agence d'évaluation des technologies et des modes d'intervention en santé [AETMIS], 2003; Amlani, 2001; Bentler, 2005). Whereas the magnitude of improvement observed with directional microphones varied across studies, reviews by AETMIS (2003), Amlani (2001), and Bentler (2005) all reported that overall directional microphones did provide a statistically significant improvement in speech recognition across studies with adults. In general, the largest improvements in speech recognition were observed for experimental conditions where the stimuli are presented in front of the listener and the noise source was fixed behind the listener. "
    [Show abstract] [Hide abstract]
    ABSTRACT: PURPOSE: The purpose of this evidence-based systematic review was to evaluate the efficacy of digital noise reduction and directional microphones for outcome measures of audibility, speech recognition, speech and language, and self- or parent-report in pediatric hearing aid users. METHOD: Twenty-six databases were searched for experimental studies published after 1980 addressing one or more clinical questions and meeting all inclusion criteria. Studies were evaluated for methodological quality, and p-values and effect sizes were reported or calculated when possible. RESULTS: A systematic search of the literature resulted in the inclusion of four digital noise reduction and seven directional microphone studies (in nine journal articles) that addressed speech recognition, speech and language, and/or self- or parent-report outcomes. No digital noise reduction or directional microphone studies addressed audibility outcomes. CONCLUSIONS: Based on a moderate level of evidence, digital noise reduction was not found to improve or degrade speech understanding. Additional research is needed before conclusions can be drawn regarding the impact of digital noise reduction on important speech, language, hearing, and satisfaction outcomes. Moderate evidence also indicates that directional microphones resulted in improved speech recognition in controlled optimal settings; however, additional research is needed to determine the effectiveness of directional microphones in actual everyday listening environments.
    American Journal of Audiology 08/2012; 21(2). DOI:10.1044/1059-0889(2012/12-0014) · 1.07 Impact Factor