Directional Microphone Research Articles

Acoustic- Versus Intelligibility-Based Assessment of Subjective Listening Difficulty Measured With the Repeat-Recall Test

Objectives: To contrast interpretations of listening effort ratings when judged against acoustic- versus intelligibility-based normative references. Design: Existing data collected from 66 normal-hearing adult listeners, comprising 2730 trials of the Repeat-Recall Test, were used to establish norms of subjective listening effort ratings for six ranges of intelligibility. Data from 21 aided hearing-impaired listeners were then used to contrast intelligibility-based norms against acoustic-based norms when interpreting listening effort ratings measured in omnidirectional and directional microphone conditions. Results: Whereas acoustic-based norms effectively demonstrated reduced effort for directional versus omnidirectional microphone modes, intelligibility-based references controlled for listeners’ performance biases and improved the consistency with which subjective ratings were ranked across the two microphone conditions. Conclusions: The choice of normative reference should be carefully considered when judging listening effort ratings from hearing-impaired individuals against those of their normal-hearing peers. Whereas acoustic-based references may be more useful for evaluating the benefits of hearing aid technology, intelligibility-based references may be better suited to identifying listeners with poor subjective experiences for speech-in-noise related to factors beyond intelligibility.

Long-Range Bird Species Identification Using Directional Microphones and CNNs

This study explores the integration of directional microphones with convolutional neural networks (CNNs) for long-range bird species identification. By employing directional microphones, we aimed to capture high-resolution audio from specific directions, potentially improving the clarity of bird calls over extended distances. Our approach involved processing these recordings with CNNs trained on a diverse dataset of bird calls. The results demonstrated that the system is capable of systematically identifying bird species up to 150 m, reaching 280 m for species vocalizing at frequencies greater than 1000 Hz and clearly distinct from background noise. The furthest successful detection was obtained at 510 m. While the method showed promise in enhancing the identification process compared to traditional techniques, there were notable limitations in the clarity of the audio recordings. These findings suggest that while the integration of directional microphones and CNNs for long-range bird species identification is promising, further refinement is needed to fully realize the benefits of this approach. Future efforts should focus on improving the audio-capture technology to reduce ambient noise and enhance the system’s overall performance in long-range bird species identification.

State-of-the-Art on the Impact of Bimodal Acoustic Stimulation on Speech Perception in Noise in Adults: A Systematic Review.

Bimodal stimulation (BS), which combines the use of a cochlear implant (CI) in one ear and a hearing aid (HA) in the opposite ear, is an established strategy to treat hearing loss by exploiting the unique capabilities of each device. CIs stimulate the auditory nerve by bypassing damaged hair cells, while HAs amplify sounds by requiring a functional hearing residual. The aim of this systematic review is to investigate the advantages and disadvantages of BS such as speech perception in noise. We examined clinical studies published from October 2020 to July 2024, following the PRISMA guidelines, focusing on the advantages and disadvantages of BS on speech perception in noise in adulthood. BS in adult patients significantly improves speech perception in quiet and noisy environments, especially for those with increased residual hearing. Unilateral CIs and BS perform similarly in quiet conditions, but BS significantly improves speech discrimination in noisy environments if loudness between the two devices is appropriately balanced. Directional microphones and programming software are new technologies that succeed in reducing environmental noise and improving verbal perception outcomes, although their features in the literature are controversial. In addition, the individuals using BS may face temporal mismatches mainly due to differing device latencies, affecting sound localization. Compensating for these mismatches can enhance localization accuracy. However, modulated noise remains a significant obstacle to verbal perception in noise. Valuable assessment tools such as music tests provide further information on hearing performance and quality of life. More research is needed to define certain selection criteria.

Comparing detection accuracy of mountain chickadee (Poecile gambeli) song by two deep-learning algorithms

The use of autonomous recording units (ARUs) has become an increasingly popular and powerful method of data collection for biological monitoring in recent years. However, the large-scale recordings collected using these devices are often nearly impossible for human analysts to parse through, as they require copious amounts of time and resources. Automated recognition techniques have allowed for quick and efficient analysis of these recordings, and machine learning (ML) approaches, such as deep learning, have greatly improved recognition robustness and accuracy. We evaluated the performance of two deep-learning algorithms: 1. our own custom convolutional neural network (CNN) detector (specialist approach) and 2. BirdNET, a publicly available detector capable of identifying over 6,000 bird species (generalist approach). We used audio recordings of mountain chickadees (Poecile gambeli) collected from ARUs and directional microphones in the field as our test stimulus set, with our custom detector trained to identify mountain chickadee songs. Using confidence thresholds of 0.6 for both detectors, we found that our custom CNN detector yielded higher detection compared to BirdNET. Given both ML approaches are significantly faster than a human detector and the custom CNN detector is highly accurate, we hope that our findings encourage bioacoustics practitioners to develop custom solutions for targeted species identification, especially given the availability of open-source toolboxes such as Koogu.

Hearing Aid apps: are they safe, practical and beneficial for children and teens in challenging situations?

An adult version of an app giving users the control over the level of the volume, microphone directionality and noise reduction was adapted for children. The main purpose of this study was to evaluate the effect of changes made to microphone directionality and noise reduction in the myPhonak Junior (the app) on Speech intelligibility in challenging listening environments in children and teens. The randomized, non-blinded interventional study with a single group of subjects involved two study visits with a home trial in-between. In the final study session speech assessment in noise was conducted in three different, randomly assigned conditions: default mode (Autosense Sky OS), preffered (self-adjusted) and the extreme condition. Questionnaire based assessment was conducted to assess the subjective benefit of using the app in different daily situations. The best scores (speech results in noise) were achieved with the preferred setting and the default Autosense Sky OS setting was significantly better than the extreme setting. The self-reported benefit through the questionnaire indicates significantly better result when adjusting the hearing aids through the app. The app is an easy-to-use way of controlling the level of noise reduction and the beam forming for children 11 years and older. It has the potential to help customizing the hearing aids beyond the default setting and helping to improve speech understanding in noise.

Factors in the Effective Use of Hearing Aids among Subjects with Age-Related Hearing Loss: A Systematic Review.

Objectives: Investigate factors contributing to the effective management of age-related hearing loss (ARHL) rehabilitation. Methods: A systematic review was conducted following PRISMA guidelines. The protocol was registered in PROSPERO (CRD42022374811). Articles were identified through systematic searches in the Scopus, PubMed, Web of Science, and Cochrane databases in May 2024. Only articles published between January 2005 and May 2024 were included. Studies were assessed for eligibility by two independent researchers and evaluated using the Crowe Critical Appraisal Tool v1.4 (CCAT). Results: Of the 278 articles identified, 54 were included. Three factors explain effective HA use. First, hearing aid signal processing, with directional microphones and noise reduction, improves user comfort and understanding regarding noise. Second, there is hearing aid fitting, with the NAL prescription rules as the gold standard, and bilateral, high-level HA performance for spatial localization and noise comprehension. Third, there is a patient-centered approach, using patient-related outcome measures (PROMs), questionnaires, counseling, and regular follow-up to involve patients in their therapeutic rehabilitation. Conclusions: Reaching a consensus on acoustic parameters is challenging due to variability in audiological results. Involving patients in their rehabilitation, addressing their needs and expectations, and offering individualized care are crucial.

Towards acoustic monitoring of bees: wingbeat sounds are related to species and individual traits.

Global pollinator decline urgently requires effective methods to assess their trends, distribution and behaviour. Passive acoustics is a non-invasive and cost-efficient monitoring tool increasingly employed for monitoring animal communities. However, insect sounds remain highly unexplored, hindering the application of this technique for pollinators. To overcome this shortfall and support future developments, we recorded and characterized wingbeat sounds of a variety of Iberian domestic and wild bees and tested their relationship with taxonomic, morphological, behavioural and environmental traits at inter- and intra-specific levels. Using directional microphones and machine learning, we shed light on the acoustic signature of bee wingbeat sounds and their potential to be used for species identification and monitoring. Our results revealed that frequency of wingbeat sounds is negatively related with body size and environmental temperature (between-species analysis), while it is positively related with experimentally induced stress conditions (within-individual analysis). We also found a characteristic acoustic signature in the European honeybee that supported automated classification of this bee from a pool of wild bees, paving the way for passive acoustic monitoring of pollinators. Overall, these findings confirm that insect sounds during flight activity can provide insights on individual and species traits, and hence suggest novel and promising applications for this endangered animal group. This article is part of the theme issue 'Towards a toolkit for global insect biodiversity monitoring'.

Chapter 3: Setting the Hearing Aid Response and Verifying Signal Processing and Features in the Test Box.

The test box can be used for fitting hearing aids (verifying audibility for the individual), for setting and fine-tuning specific signal processing (e.g., directional microphones, noise reduction, frequency lowering, telecoil responses), and for setting the response for specific accessories (e.g., remote microphones). If you have selected these features for your patient, it is important to make sure they are working properly and turned on. In addition, these tests can help you address specific patient complaints. Let us start by using the test box to pre-set a hearing aid and then we will move on to speech tests of signal processing and features.

Hearing Aid Fitting and Fine-tuning Strategies Implemented by Certified Audiologists in India

Background: Management of hearing-impaired individuals using hearing aids requires expertise in fitting formulas, compression methods, frequency adjustments, microphone directionality, noise reduction algorithms, and feedback management. There are abundant online resources/guidelines for programming and fine-tuning hearing aids. The fitting strategies for hearing aids can differ among professionals based on their expertise and convenience. Aims and Objectives: The survey study aimed to gain comprehension of the methods used by audiologists practicing in Indian subcontinent in choosing, fitting, and tuning hearing aids for adults with hearing impairment. Materials and Methods: A web-based survey with a 25-item questionnaire was carried out among audiologists nationwide, addressing topics such as hearing aid selection and fitting techniques. Among the audiologists practicing in India, 77 audiologists from various workplaces across India responded to the survey. The data gathered were then subjected to descriptive analysis. Results: The study showed that the selection of hearing aids depended on the extent of hearing loss and the main listening needs of the person. Audiologists generally used manufacturers’ initial fit and their expertise to adjust different signal processing features and considered patient feedback for additional adjustments. Most audiologists use only pure-tone audiometry for the initial evaluation of hearing abilities. Conclusion: The findings of the research underscore the absence of standardized procedures for audiologists in the fitting of hearing aids, considering the numerous signal-processing approaches present in contemporary hearing technology. Despite exponential advancements in hearing aid technology, there remains a scarcity of concise and accessible information that would enable audiologists to utilize such sophisticated technologies during fitting and tuning effectively.

Modeling the relationship between listener factors and signal modification: A pooled analysis spanning a decade

The overarching goal of our work is to understand how listeners respond to hearing aid processing and consequently inform individualized hearing aid treatment. Our previous work demonstrated that individual cognitive abilities, age, and hearing loss contribute to variability in response to cumulative signal modifications introduced by hearing aid processing and background noise. Specifically, older individuals with poorer working memory and more hearing loss were more susceptible to signal modifications introduced by hearing aid processing. These relationships were established in independent studies involving systematic manipulations of compression, digital noise reduction, frequency lowering, or microphone directionality. In this study, we present a hierarchical pooled analysis of data collected from six previous studies to develop a unified statistical model of the relationships between response to signal modification and individual listener variables. Across studies, signal modification is quantified using a cepstral correlation metric that accounts for cumulative envelope distortions arising from hearing aid processing and background noise. The statistical model will determine how working memory, age, and degree of hearing loss mediate the relationship between signal modification and speech intelligibility in noise across a large dataset. Both inferential and predictive applications of the combined data and model will be discussed. [Work supported by NIDCD.]

The theoretical maximum intelligibility improvement that can be provided by hearing aids

One goal of hearing aids is to increase the intelligibility of speech by improving the signal-to-noise ratio through the use of directional microphones and/or digital noise reduction. With this objective in mind, an ideal hearing aid would output amplified target speech with a signal-to-noise ratio of +∞. However, even in this ideal scenario, vent effects would allow background noise to enter the ear canal via the direct sound path while also allowing amplified sound to escape from the ear canal. In this experiment, a range of hearing aid fittings were simulated to account for these vent effects. Hearing-impaired listeners were tested using the ideal simulated hearing aid, and the results will show the maximum theoretical hearing aid benefit.

A Survey of Recent Advances in Hearing Aid Technologies and Trends

Hearing aids are small electronic devices worn in or behind the ear to amplify sound for individuals with hearing loss. They work by capturing sound through a microphone, processing it electronically, and then delivering it through a speaker into the ear canal. Modern hearing aids come with various features like noise reduction, directional microphones, and wireless connectivity, making them more effective and convenient for users. This survey paper provides an overview of recent advances in hearing aid technologies, exploring the evolving landscape of assistive devices designed to improve the auditory experience for individuals with hearing impairments. The paper reviews key aspects of hearing aids, including signal processing techniques, device designs, connectivity options, and user-centric features. The survey encompasses highlighting innovative solutions aimed at addressing the diverse needs of hearing-impaired individuals.

Do Different Types of Microphones Affect Listening Effort in Cochlear Implant Recipients? A Pupillometry Study.

It is known that subjects with a cochlear implant (CI) need to exert more listening effort to achieve adequate speech recognition compared to normal hearing subjects. One tool for assessing listening effort is pupillometry. The aim of this study is to evaluate the effectiveness of adaptive directional microphones in reducing listening effort for CI recipients. We evaluated listening in noise and listening effort degree (by pupillometry) in eight bimodal subjects with three types of CI microphones and in three sound configurations. We found a correlation only between sound configurations and listening in noise score (p-value 0.0095). The evaluation of the microphone types shows worse scores in listening in noise with Opti Omni (+3.15 dB SNR) microphone than with Split Dir (+1.89 dB SNR) and Speech Omni (+1.43 dB SNR). No correlation was found between microphones and sound configurations and within the pupillometric data. Different types of microphones have different effects on the listening of CI patients. The difference in the orientation of the sound source is a factor that has an impact on the listening effort results. However, the pupillometry measurements do not significantly correlate with the different microphone types.

Speech Understanding and Subjective Listening Effort in Noise With Different OTEs and Sound Processing Technologies.

To determine speech reception thresholds (SRTs) in noise and subjective listening effort (LE) in cochlear implant (CI) recipients for application of three sound processing (SP) technologies with two off-the-ear (OTE) CI sound processors, a fixed moderately directional microphone (Standard), an adaptive directional microphone (Beam), and the spatial noise-reduction setting ForwardFocus, with the Kanso 2 (OTE2), and Beam with the Kanso (OTE1). Prospective repeated measures, within-subject design. Single tertiary-referral center. Twenty CI recipients with bilateral severe-to-profound sensorineural hearing loss. SRTs were assessed in two spatial configurations with frontal speech and noise from 90-180-270 degrees (S0N90-180-270) or from the CI side (S0NCI). SRTs were obtained for sentences of the Oldenburg sentence test presented in International Collegium of Rehabilitative Audiology (ICRA) noise ICRA5-250. LE for speech understanding in noise was evaluated in S0N90-180-270 and assessed in effort scale categorical units (ESCUs) by using Adaptive Categorical Listening Effort Scaling (ACALES). LEs at 5-dB signal-to-noise ratio (SNR) were calculated from fitted psychometric curves. With OTE2 in S0N90-180-270, SRT with ForwardFocus (-4.28 dB SNR) was better than with Beam (-3.13 dB SNR) and Standard (0.43 dB SNR). ForwardFocus showed lower LE5dB (2.61 ESCU) compared with Beam (4.60 ESCU) and Standard (5.32 ESCU). In a comparison of both OTEs in S0N90-180-270 regarding best-performing SP technology, ForwardFocus with OTE2 yielded a better SRT and better LE5dB than Beam with OTE1 (SRT: -1.70 dB SNR; LE5dB: 4.00 ESCU). With OTE2 in S0NCI, SRT was improved with ForwardFocus (-2.78 dB SNR) compared with Beam (-1.23 dB SNR) and Standard (1.83 dB SNR). With respect to SP technology and OTE, CI recipients experience best SRT and lowest LE in S0N90-180-270 when using ForwardFocus with OTE2. ACALES is feasible for assessing subjective LE in CI recipients.

Measuring directivity of half-inch measurement microphones

The directivity of a microphone is the relative sensitivity variation as a function of incidence angle. This is an important characteristic when every sound arriving at the microphone position is relevant. This paper presents the measuring directivity of half-inch measurement microphones. The microphone is placed in a free sound field and exposed to a sound pressure. The unloaded output voltage is measured. Then, the microphone is rotated in 30o steps, while both the acoustic centers of the microphone and the sound source remain in fixed positions in the sound field, and is exposed to the same sound pressure. The unloaded output voltage for each angle of incidence is measured and them the difference relative to 0 deg. of incidence is calculated as a function of frequency. The directivity of eight measurement microphones from the same manufacturer but of different types and frequency response characteristics (i.e. pressure field, random incidence or free-field) were measured. Results showed that the microphones object of this investigation have similar directivities in the frequency range from 16 Hz to 12.5 kHz regardless of their frequency response characteristics.

Design of frequency-invariant uniform concentric circular arrays with first-order directional microphones

Most of the existing frequency-invariant beamformers (FIBs) with circular arrays are implemented with omnidirectional microphones, where uniform circular arrays (UCAs) and uniform concentric circular arrays (UCCAs) have been widely utilized. However, the resulting FIB usually suffers from the deep nulls problem in the white noise gain (WNG) and the white noise amplification problem at low frequencies even if the order of the target beampattern is one. Due to its simple implementation, first-order directional microphones are adopted to improve the robustness of the FIB with UCCAs (FIB-UCCAs) in this paper. We exploit the circular harmonics decomposition rather than the Jacobi–Anger expansion to approximate the beampattern of the FIB-UCCAs with first-order directional microphones, because the directivity pattern of directional microphones is related to the direction of the signal. We show that the FIB-UCCAs can completely avoid the deep nulls problem in the WNG as long as the ring with the largest radius utilizes first-order directional microphones. In addition, the white noise amplification problem at low frequencies can be greatly alleviated if first-order directional microphones are utilized. Specifically, we show that the inherent white noise amplification problem at low frequencies can be completely circumvented when the order of the desired beampattern is one.

Design and Performance Evaluation of a Directional Telescopic Microphone for Enhanced Environmental Sound Capture

A directional telescopic microphone is composed of two parts. One is the pick-up circuit made up of 34 different length aluminum tubes to respond in a specific frequency. The use of a sensitive FET mic is to pick up a sound from a direction. The signal from the FET mic will be feed to the microphone preamplifier in order to amplify the signal. The Equalization and Attenuation circuit is responsible for the balancing and boosting the low and high frequency. The pick-up signal can be easily recordedto a device through the recording unit or can be heard through the speaker, driven by a power amplifier in order to set up the signal. The main purpose of the gadget is to be used in an environmental study. This can pick up sound that was not normally heard by human ear in a specify distance.

Paediatric amplification protocol, based on individualization of the hearing aids’ fitting parameters

Background. There are no paediatric amplification clinical practice guidelines in Russia at the moment. At the same time the technological progress of hearing aids (HA), new algorithms and functions requires the objective evidence of safety and effectiveness for the hearing impaired children. For these reasons paediatric amplification algorithm was developed by the authors. Besides the standard procedures the algorithm includes an objective electroacoustic verification of the output parameters and separate HA functions. The research is devoted to the investigation of the protocols advantages. 
 Aim development and evaluation the paediatric amplification protocol, based on objective electroacoustic verification of the output and functions of hearing aid. 
 Materials and Methods. Prospective, randomized, controlled clinical trial was performed. Two protocols effectiveness were compared. Standard protocol (control group) is based on the subjective verification. Experimental protocol suggests an electroacoustic verification of the output and different HA functions: feedback cancellation, amplitude and frequency compression, microphone directionality, digital noise reduction (experimental group). Each group included 56 children (317 years old) with permanent hearing loss from moderate to moderately-severe degree. Initial amplification was performed for each child; the results were estimated in 1, 3 and 6 months using PEACH and LIFE questionnaires, speech audiometry and phoneme testing. DataLogging and first fitting appointment time were also estimated. 
 Results. In preschool-age children of the experimental group post-amplification PEACH results were 6% better than in controls. In school-age children (LIFE questionnaire) results were 11% better comparing with control group. Speech intelligibility in quiet was 3.1% (p 0.05) higher for pre-schoolers in the experimental group and 9.3% (p 0.01) higher for school-age children comparing with control group. Speech intelligibility in noise was higher in experimental group than in control: 7.8% (p 0.05) in pre-schoolers and 13% (p 0.01) for school-age children. Phoneme recognition was better in experimental group as well: 4.5% (p 0.05) in pre-schoolers and 9.8% (p 0.01) in school-agers than in control group. After HA fitting following an experimental protocol DataLogging time was 1112% longer in comparison with standard procedure. On the other hand, experimental protocol took in average 1.5 hours for the first fitting and standard protocol 53 minutes. 
 Conclusions. Protocol of paediatric amplification based on objective electroacoustic verification of HA output and functions allows to significantly increase the effectiveness of hearing rehabilitation in children.

Direction-of-arrival and power spectral density estimation using a single directional microphone and group-sparse optimization

In this paper, two approaches are proposed for estimating the direction of arrival (DOA) and power spectral density (PSD) of stationary point sources by using a single, rotating, directional microphone. These approaches are based on a method previously presented by the authors, in which point source DOAs were estimated by using a broadband signal model and solving a group-sparse optimization problem, where the number of observations made by the rotating directional microphone can be lower than the number of candidate DOAs in an angular grid. The DOA estimation is followed by the estimation of the sources’ PSDs through the solution of an overdetermined least squares problem. The first approach proposed in this paper includes the use of an additional nonnegativity constraint on the residual noise term when solving the group-sparse optimization problem and is referred to as the Group Lasso Least Squares (GL-LS) approach. The second proposed approach, in addition to the new nonnegativity constraint, employs a narrowband signal model when building the linear system of equations used for formulating the group-sparse optimization problem, where the DOAs and PSDs can be jointly estimated by iterative, group-wise reweighting. This is referred to as the Group-Lasso with l_1-reweighting (GL-L1) approach. Both proposed approaches are implemented using the alternating direction method of multipliers (ADMM), and their performance is evaluated through simulations in which different setup conditions are considered, ranging from different types of model mismatch to variations in the acoustic scene and microphone directivity pattern. The results obtained show that in a scenario involving a microphone response mismatch between observed data and the signal model used, having the additional nonnegativity constraint on the residual noise can improve the DOA estimation for the case of GL-LS and the PSD estimation for the case of GL-L1. Moreover, the GL-L1 approach can present an advantage over GL-LS in terms of DOA estimation performance in scenarios with low SNR or where multiple sources are closely located to each other. Finally, it is shown that having the least squares PSD re-estimation step is beneficial in most scenarios, such that GL-LS outperformed GL-L1 in terms of PSD estimation errors.

Acoustical verification of binaural features in hearing aids

Hearing aid verification systems are designed to verify sound pressure levels in a patient’s ear canal, as well as ensure hearing aid features are performing to company specifications. In addition to verifying sound output, verification systems can analyze frequency specific compression, prescription targets, directional microphones, noise reduction performance, etc. However, current verification systems are unable to verify several advanced digital signal processing (DSP) features that companies have included in their hearing aids over the recent years. Particularly, binaural features which require both hearing aids to be analyzed simultaneously to measure interaural cues. Here, interaural cues were analyzed from recordings made on an acoustic manikin in an anechoic chamber across various noise reduction and directional microphone features using open-fit and occluding coupling compared to an unaided condition. During data collection, settings in the fitting software did not always align to hearing aid coupling (i.e., open versus occluding dome conditions), an error likely to occur clinically. For some noise reduction hearing aid conditions, a large interaural level difference (ILD) was introduced to one hearing aid, distorting the sound source location. ILD cues measured here, across different DSP and coupling conditions, suggest verification protocols should include additional features, such as binaural measurements.