Andrew Dittberner

Predictive Measures of Directional Benefit Part 2: Verification of Different Approaches to Estimating Directional Benefit

Objective: In this investigation, the relation between various directivity measures and subject performance with directional microphone hearing aids was determined. Design: Test devices included first- and second-order directional microphones. Recordings of sentences and noise (Hearing in Noise Test, HINT) were made through each test device in simple, complex, and anisotropic background noise conditions. Twenty-six subjects, with normal hearing, were administered the HINT test recordings and directional benefit was computed. These measures were correlated to theoretical, free-field, and Knowles Electronic Manikin for Acoustic Research (KEMAR) directivity index (DI) values, as well as front-to-back ratios (FBR), in situ signal-to-noise ratios (SNR), and a newly proposed Db SNR, wherein a predictive value of the SNR improvement is calculated as a function of the noise source incidence. Results: The different predictive scores showed high correlation to the measured directional benefit scores in the complex (diffuse-like) background noise condition (r = 0.89 to 0.97, p < 0.05) but not across all background noise conditions (r = 0.45 to 0.97, p < 0.05). The Db SNR approach and the in situ SNR measures provided excellent prediction of subject performance in all background noise conditions (0.85 to 0.97, p < 0.05). None of the predictive measures could account for the effects of reverberation on the speech signal (r = 0.35 to 0.40, p < 0.05). Conclusions: For environments that included a discrete number of noise sources, the in situ SNR and Db SNR estimates were most predictive of subject performance. No predictive approach was indicative of the directional benefit achieved when the speech was also subjected to reverberation (temporal distortion). This finding has implications for real-world estimates of directional benefit.

Predictive measures of directional benefit part 1: estimating the directivity index on a manikin.

Objective: In this investigation, a method for computing a directivity index (DI) on a manikin for directional microphones in hearing aids was proposed and evaluated comparatively to other conventional methods. Design: Test devices included first- and second-order directional microphones. Signal presentation, implemented in an anechoic chamber, involved a single noise source rotated completely around the directional microphone in a hearing aid, in free field and on a manikin, at a defined radius. The area covered was equivalent to the approximate surface area of a sphere. It was anticipated that an equal angular resolution of 10° (elevation and azimuth) would effectively estimate the DI of first-, second-, and higher-order directional microphone systems located in a hearing aid on a manikin. A total of 450 spatially varied presentation points were analyzed, each weighted in reference to direction of arrival on the directional microphone. Results: Empiric differences between the DI derived from the 3D-DI method proposed in this investigation and the conventionally derived 2D-DI method DI on a manikin were as large as 3.8 dB in the higher frequencies, depending on the device under test. Conclusions: The magnitude of these differences was dependent on the device under test microphone location. The further the microphone was placed into the ear of the manikin, the larger the empiric differences.

The Effect of Low-Level Laser Therapy on Hearing

One purported use of low-level laser therapy (LLLT) is to promote healing in damaged cells. The effects of LLLT on hearing loss and tinnitus have received some study, but results have been equivocal. The purpose of this study was to determine if LLLT improved hearing, speech understanding, and/or cochlear function in adults with hearing loss. Using a randomized, double-blind, placebo-controlled design, subjects were assigned to a treatment, placebo, or control group. The treatment group was given LLLT, which consisted of shining low-level lasers onto the outer ear, head, and neck. Each laser treatment lasted approximately five minutes. Three treatments were applied within the course of one week. A battery of auditory tests was administered immediately before the first treatment and immediately after the third treatment. The battery consisted of pure-tone audiometry, the Connected Speech Test, and transient-evoked otoacoustic emissions. Data were analyzed by comparing pre- and posttest results. No statistically significant differences were found between groups for any of the auditory tests. Additionally, no clinically significant differences were found in any individual subjects. This trial is registered with ClinicalTrials.gov (NCT01820416).

A method is proposed to evaluate directional-microphone strategies

Directional microphones on hearing instruments continue to be the primary method for improving speech understanding in noise for listeners with hearing impairment. From the first directional microphones in which all processing occurred in the acoustic domain, this technology has evolved into a complex signal processing strategy, converging with other sound processing strategies (e.g., noise reduction) in the hearing instrument. Today’s directional-microphone processing strategies are designed not only to improve directivity, but also to deal with some of the limitations of previous generations of directional-microphone products. For example, it is well known that a directional microphone’s response needs to be equalized in the low frequencies to offset the low-cut roll-off that occurs in response to a far-field sound source (i.e., sound that is generated at least a meter away from the microphone).1,2 Less well known is that such equalization also has the opposite effect, specifically with near-field noise sources, leading to unnecessary gain in the low frequencies (e.g., wind noise or user’s own voice; proximity effect). Because the unequalized microphone response can diminish the audibility of far-field sound sources for listeners, especially those with low-frequency hearing loss, clinicians often apply a fixed amount of equalization to ensure signal audibility. Unfortunately, this practice can also lead to overamplification of the low frequencies for near-field noise sources, making directional microphones undesirable for use outdoors. In addition, equalization of a directional response to that of the omnidirectional response can increase the hearing instrument’s noise floor, making it audible to some listeners in quiet environments. To solve some of these limitations in directional systems, directional-microphone algorithms have become more adaptive so they automatically adjust for such things as the roll-off equalization. Adaptively compensating for frequency roll-off not only ensures audibility for far-field sounds, but also prevents the noise floor level from exceeding the ambient noise level or wind noise from sounding louder with a directional microphone than an omnidirectional microphone. Due to the adaptive and multifunctional approaches used in directional-microphone strategies, it is difficult to ensure that only the sound processing related to directionality is active and other sound processing that may interfere with measuring directivity is deactivated. Some manufacturers’ fitting software does not allow for deactivating interfering sound processing. Sometimes there may be interfering sound processing that the person measuring directivity for a particular hearing instrument is unaware of. Being aware of these issues is essential to making objective and equal comparisons of hearing instruments and understanding the strengths and limitations of each. Current standards, such as ANSI S3.35,3 define a measure to characterize a particular trait, such as directionality, for a given hearing aid. Yet, such standards assume that the instrument can be set to perform a single function, such as directionality, without other sound processing strategies biasing the results. The purpose of this article is to present a method to evaluate current directional-microphone strategies, both fixed (time-invariant) and adaptive (time-variant). This method does not replace the suggested ANSI S3.35 standard, but rather uses the logic in that standard to provide a uniform test environment where one can compare different directionalmicrophone processing strategies, fixed or adaptive. In other words, it is a relative (i.e., comparative) measure of directivity, whereas the ANSI S3.35 method is an absolute

An objective metric for describing the basic acoustics of binaural directivity patterns in humans

It is accepted knowledge that having two ears are better than one when trying to listen to a signal of interest in the presence of spatially-separated noise sources (e.g. Blauert, 1997; Bregman, 1994; Zurek, 1993). Models have been proposed purporting of the benefits of the head shadow effect, binaural interactions, and cognitive factors that explain how one can understand sound with linguistic or other contextual meaning better in the presence of spatially-separate noise sources. However, less discussed is the attribute of human listeners having the ability to also hear and identify sound sources, seemingly on demand, that occur around them, a condition made possible by the fact of having two ears. Zurek (1993) proposed and discussed at length on the directivity effects of binaural listening (e.g., Better Ear Strategy). What is proposed in this study is an extension to this model to include the omni-directional directivity effects of binaural listening to describe the listener’s ability to remain connect...

Calibration and acoustic performance of sparse transducer array

In a previous research, a theoretical approach has been taken to predict, form, and optimize acoustic beam patterns from a sparse array of transducers. The current objective is to compare these theoretical results to experimentally obtained results from an assembled sparse array of transmit transducers. The array design and calibration procedure is presented. Acoustic beam patterns of the assembly are measured and compared to the theoretical model. Limitations of the array’s performance are evaluated.In a previous research, a theoretical approach has been taken to predict, form, and optimize acoustic beam patterns from a sparse array of transducers. The current objective is to compare these theoretical results to experimentally obtained results from an assembled sparse array of transmit transducers. The array design and calibration procedure is presented. Acoustic beam patterns of the assembly are measured and compared to the theoretical model. Limitations of the array’s performance are evaluated.

Situational awareness assessment of hearing protection

Uncompromised situational awareness has become a critical component of hearing protection devices (HPDs). Situational awareness is a complex psychological phenomenon, which consists of several perceptual and cognitive factors. This study presents data from three experiments designed to analyze the performance of HPDs on measures of situational awareness and determine how multiple factors may impact in-the-field performance. Data are presented for four hearing protection devices on measures of sound localization, distance perception, spatial segregation, speech intelligibility, and dynamic scene analysis. Baseline (open-ear) data is also presented to contrast with the HPDs. Small differences in fine localization-discrimination and the number of large quadrant errors were observed, but these differences between devices were not observed in the more complex scene analysis task. A performance index was developed to determine overall performance of each HPD compared to open-ear performance. This index combined...

The quest for good, quiet spaces: Evaluating the relationship between office noise annoyance, distraction, and performance

To facilitate office work performance, acousticians must design spaces that minimize annoyance from background noise, primarily from HVAC equipment, and reduce worker distraction caused by intermittent sounds, e.g., ringing telephones. Increasing background noise can mask intermittent sounds and mitigate distraction, but negatively affects annoyance. Additionally, some disrupting sounds, such as alarms, contain informational content necessary for workplaces. Balancing worker annoyance and distraction can be difficult since the definition of what constitutes a good, quiet space is yet unclear. The goal of the present work was to perform a literature review to inform ideal office noise conditions and develop an experimental procedure to test such environments. The review included papers about indoor environmental quality and the effects of acoustics on environmental satisfaction, job performance, and noise annoyance, as well as cognitive, neurobehavioral, and physiological measures that can quantify work pe...

Balancing the detrimental effects of office noise annoyance and distraction on work performance

Broadband, steady-state background noise can improve open office conditions by facilitating speech privacy and reducing distraction caused by intermittent, occupancy-generated noise. The background noise is typically generated by HVAC systems, though can be added with loudspeakers to boost speech masking. However, too high background noise levels can cause annoyance, fatigue, and other noise-related symptoms. It is yet unclear whether noise annoyance or distraction impairs work performance more. This study investigated the trade-off between noise annoyance and distraction, as well as their effects on acoustic dissatisfaction and performance. Subjects performed cognitive tasks while exposed to simulated office acoustic environments reproduced using higher-order Ambisonics. At fixed time intervals, the subjects could change the acoustic environment by adjusting either the background or intermittent noise levels. Lowering background noise caused the intermittent noise to rise, and vice versa. By the end of testing, it was expected that each subject equalized their dissatisfactions of the two noise types. Annoyance and distraction were assessed with a survey at each time interval. Physiological measures, including heart rate variability and skin conductance, were collected to correlate arousal/stress levels with each acoustic environment. The results of the study may provide context to effectively utilize background noise in open-plan offices.Broadband, steady-state background noise can improve open office conditions by facilitating speech privacy and reducing distraction caused by intermittent, occupancy-generated noise. The background noise is typically generated by HVAC systems, though can be added with loudspeakers to boost speech masking. However, too high background noise levels can cause annoyance, fatigue, and other noise-related symptoms. It is yet unclear whether noise annoyance or distraction impairs work performance more. This study investigated the trade-off between noise annoyance and distraction, as well as their effects on acoustic dissatisfaction and performance. Subjects performed cognitive tasks while exposed to simulated office acoustic environments reproduced using higher-order Ambisonics. At fixed time intervals, the subjects could change the acoustic environment by adjusting either the background or intermittent noise levels. Lowering background noise caused the intermittent noise to rise, and vice versa. By the end of t...

Better‐ear listening strategies for normal‐hearing and hearing‐impaired individuals

The current study was designed to examine how hearing‐impaired (HI) listeners use better‐ear listening. Better‐ear performance was initially assessed for normal‐hearing (NH) and HI participants using a connected‐speech recognition test at two signal‐to‐noise‐ratio (SNR) levels presented over insert earphones. Test conditions consisted of monaural, symmetric and asymmetric combinations of better and worse SNR conditions. SNRs were different for NH and HI groups. Stimuli were presented at each participants most comfortable level; to account for audibility with HI participants, stimuli were spectrally shaped based on audiometric data. A second experiment investigated the role of spatial information using recordings of the same stimuli presented in a sound‐dampened chamber at the same SNR differences, with the speech signal at 0° azimuth/elevation, and uncorrelated babble presented from eight speakers at the corners of the chamber. Listening strategies between NH and HI groups were similar across experiments...