Spatial hearing rendering in wireless microphone systems for binaural hearing aids

In 2015, 360 million people, including 32 million children, were suffering from hearing impairment all over the world. This makes hearing disability a major worldwide issue. In the US, the prevalence of hearing loss increased by 160% over the past generations. However, 72% of the 34 million impaired American persons (11% of the population) still have an untreated hearing loss. Among the various current solutions alleviating hearing disability, hearing aid is the only non-invasive and the most widespread medical apparatus. Combined with hearing aids, assisting listening devices are a powerful answer to address the degraded speech understanding observed in hearing-impaired subjects, especially in noisy and reverberant environments. Unfortunately, the conventional devices do not accurately render the spatial hearing property of the human auditory system, weakening their benefits. Spatial hearing is an attribute of the auditory system relying on binaural hearing. With 2 ears, human beings are able to localize sounds in space, to get information about the acoustic surroundings, to feel immersed in environments... Furthermore, it strongly contributes to speech intelligibility. It is hypothesized that recreating an artificial spatial perception through the hearing aids of impaired people might allow for recovering a part of these subjects' hearing performance. This thesis investigates and supports the aforementioned hypothesis with both technological and clinical approaches. It reveals how certain well-established signal processing methods can be integrated in some assisting listening devices. These techniques are related to sound localization and spatialization. Taking into consideration the technical constraints of current hearing aids, as well as the characteristics of the impaired auditory system, the thesis proposes a novel solution to restore a spatial perception for users of certain types of assisting listening devices. The achieved results demonstrate the feasibility and the possible implementation of such a functionality on conventional systems. Additionally, this thesis examines the relevance and the efficiency of the proposed spatialization feature towards the enhancement of speech perception. Via a clinical trial involving a large number of patients, the artificial spatial hearing shows to be well appreciated by disabled persons, while improving or preserving their current hearing abilities. This can be considered as a prominent contribution to the current scientific and technological knowledge in the domain of hearing impairment

The implications of leisure noise for young people with hearing impairment.

There is scientific evidence that some leisure activities involve potentially hazardous noise. This cross-sectional cohort study was the first to investigate the implications of leisure-noise exposure for young people with early hearing impairment (HI). Participants (n = 268) were surveyed about health, leisure participation, attitudes to noise, hearing aid use and hearing protective strategies. Hearing threshold level (HTL) and other clinical data were collected. Leisure data were used to estimate individual whole-of-life noise exposure. Attitudes to noise, leisure participation and noise exposure data were compared with those of an age-matched cohort with 'normal' (non-impaired) hearing (NH). The attitudes towards noise risk of parents of children in the HI participant group, and parents of children with NH, were also surveyed and compared. Although almost 50% of participants (without specific risk factors for progressive hearing loss) had experienced HTL shift, an association between HTL shift and whole-of-life noise exposure was not observed. The interpretation of this finding was limited by the generally conservative noise exposure of participants with HI. Leisure activity profiles and whole-of-life noise exposure of adolescents (13-17 yrs) with HI and NH were similar, and few were considered at high noise-injury risk. Young adults (18-24 yrs) with HI participated less than their peers with NH in some social activities and accumulated noise exposure was lower overall than for the NH group. Only 9% of the young adult HI group were considered "at risk" for noise injury, compared with 24% of the NH group. Parents of children with HI and NH perceived noise to be a significant risk to young people in general, but few considered their own child to be at high risk. Differences in parent permissiveness about children’s leisure participation (HI vs. NH groups) were observed. Most participants (HI and NH) also considered that leisure noise was a risk to hearing health, however, very few considered their personal risk to be “very high”, which is consistent with previous health research. Use of hearing protective strategies was low and many participants with HI reported using hearing aids (switched on) in noisy environments, which may increase accumulated noise exposure. These findings suggest that current hearing loss prevention approaches that primarily educate individuals about self-protective behaviour may be inadequate. Initiatives that aim to reduce hazardous noise may be more effective in moderating the risk of noise injury. In addition, the reduction of noise in social venues would provide more inclusive social environments for patrons with HI. With respect to the finding that participation in some social activities was lower for young adults with HI, hearing (re)habilitation goals that extend beyond the traditional considerations of language development and educational attainment may also be beneficial

Iceberg: a loudspeaker-based room auralization method for auditory research

Depending on the acoustic scenario, people with hearing loss are challenged on a different scale than normal hearing people to comprehend sound, especially speech. That happen especially during social interactions within a group, which often occurs in environments with low signal-to-noise ratios. This communication disruption can create a barrier for people to acquire and develop communication skills as a child or to interact with society as an adult. Hearing loss compensation aims to provide an opportunity to restore the auditory part of socialization. Technology and academic efforts progressed to a better understanding of the human hearing system. Through constant efforts to present new algorithms, miniaturization, and new materials, constantly-improving hardware with high-end software is being developed with new features and solutions to broad and specific auditory challenges. The effort to deliver innovative solutions to the complex phenomena of hearing loss encompasses tests, verifications, and validation in various forms. As the newer devices achieve their purpose, the tests need to increase the sensitivity, requiring conditions that effectively assess their improvements. Regarding realism, many levels are required in hearing research, from pure tone assessment in small soundproof booths to hundreds of loudspeakers combined with visual stimuli through projectors or head-mounted displays, light, and movement control. Hearing aids research commonly relies on loudspeaker setups to reproduce sound sources. In addition, auditory research can use well-known auralization techniques to generate sound signals. These signals can be encoded to carry more than sound pressure level information, adding spatial information about the environment where that sound event happened or was simulated. This work reviews physical acoustics, virtualization, and auralization concepts and their uses in listening effort research. This knowledge, combined with the experiments executed during the studies, aimed to provide a hybrid auralization method to be virtualized in four-loudspeaker setups. Auralization methods are techniques used to encode spatial information into sounds. The main methods were discussed and derived, observing their spatial sound characteristics and trade-offs to be used in auditory tests with one or two participants. Two well-known auralization techniques (Ambisonics and Vector-Based Amplitude Panning) were selected and compared through a calibrated virtualization setup regarding spatial distortions in the binaural cues. The choice of techniques was based on the need for loudspeakers, although a small number of them. Furthermore, the spatial cues were examined by adding a second listener to the virtualized sound field. The outcome reinforced the literature around spatial localization and these techniques driving Ambisonics to be less spatially accurate but with greater immersion than Vector-Based Amplitude Panning. A combination study to observe changes in listening effort due to different signal-to-noise ratios and reverberation in a virtualized setup was defined. This experiment aimed to produce the correct sound field via a virtualized setup and assess listening effort via subjective impression with a questionnaire, an objective physiological outcome from EEG, and behavioral performance on word recognition. Nine levels of degradation were imposed on speech signals over speech maskers separated in the virtualized space through Ambisonics' first-order technique in a setup with 24 loudspeakers. A high correlation between participants' performance and their responses on the questionnaire was observed. The results showed that the increased virtualized reverberation time negatively impacts speech intelligibility and listening effort. A new hybrid auralization method was proposed merging the investigated techniques that presented complementary spatial sound features. The method was derived through room acoustics concepts and a specific objective parameter derived from the room impulse response called Center Time. The verification around the binaural cues was driven with three different rooms (simulated). As the validation with test subjects was not possible due to the COVID-19 pandemic situation, a psychoacoustic model was implemented to estimate the spatial accuracy of the method within a four-loudspeaker setup. Also, an investigation ran the same verification, and the model estimation was performed with the introduction of hearing aids. The results showed that it is possible to consider the hybrid method with four loudspeakers for audiological tests while considering some limitations. The setup can provide binaural cues to a maximum ambiguity angle of 30 degrees in the horizontal plane for a centered listener

Iceberg: a loudspeaker-based room auralization method for auditory research

Depending on the acoustic scenario, people with hearing loss are challenged on a different scale than normal hearing people to comprehend sound, especially speech. That happen especially during social interactions within a group, which often occurs in environments with low signal-to-noise ratios. This communication disruption can create a barrier for people to acquire and develop communication skills as a child or to interact with society as an adult. Hearing loss compensation aims to provide an opportunity to restore the auditory part of socialization. Technology and academic efforts progressed to a better understanding of the human hearing system. Through constant efforts to present new algorithms, miniaturization, and new materials, constantly-improving hardware with high-end software is being developed with new features and solutions to broad and specific auditory challenges. The effort to deliver innovative solutions to the complex phenomena of hearing loss encompasses tests, verifications, and validation in various forms. As the newer devices achieve their purpose, the tests need to increase the sensitivity, requiring conditions that effectively assess their improvements. Regarding realism, many levels are required in hearing research, from pure tone assessment in small soundproof booths to hundreds of loudspeakers combined with visual stimuli through projectors or head-mounted displays, light, and movement control. Hearing aids research commonly relies on loudspeaker setups to reproduce sound sources. In addition, auditory research can use well-known auralization techniques to generate sound signals. These signals can be encoded to carry more than sound pressure level information, adding spatial information about the environment where that sound event happened or was simulated. This work reviews physical acoustics, virtualization, and auralization concepts and their uses in listening effort research. This knowledge, combined with the experiments executed during the studies, aimed to provide a hybrid auralization method to be virtualized in four-loudspeaker setups. Auralization methods are techniques used to encode spatial information into sounds. The main methods were discussed and derived, observing their spatial sound characteristics and trade-offs to be used in auditory tests with one or two participants. Two well-known auralization techniques (Ambisonics and Vector-Based Amplitude Panning) were selected and compared through a calibrated virtualization setup regarding spatial distortions in the binaural cues. The choice of techniques was based on the need for loudspeakers, although a small number of them. Furthermore, the spatial cues were examined by adding a second listener to the virtualized sound field. The outcome reinforced the literature around spatial localization and these techniques driving Ambisonics to be less spatially accurate but with greater immersion than Vector-Based Amplitude Panning. A combination study to observe changes in listening effort due to different signal-to-noise ratios and reverberation in a virtualized setup was defined. This experiment aimed to produce the correct sound field via a virtualized setup and assess listening effort via subjective impression with a questionnaire, an objective physiological outcome from EEG, and behavioral performance on word recognition. Nine levels of degradation were imposed on speech signals over speech maskers separated in the virtualized space through Ambisonics' first-order technique in a setup with 24 loudspeakers. A high correlation between participants' performance and their responses on the questionnaire was observed. The results showed that the increased virtualized reverberation time negatively impacts speech intelligibility and listening effort. A new hybrid auralization method was proposed merging the investigated techniques that presented complementary spatial sound features. The method was derived through room acoustics concepts and a specific objective parameter derived from the room impulse response called Center Time. The verification around the binaural cues was driven with three different rooms (simulated). As the validation with test subjects was not possible due to the COVID-19 pandemic situation, a psychoacoustic model was implemented to estimate the spatial accuracy of the method within a four-loudspeaker setup. Also, an investigation ran the same verification, and the model estimation was performed with the introduction of hearing aids. The results showed that it is possible to consider the hybrid method with four loudspeakers for audiological tests while considering some limitations. The setup can provide binaural cues to a maximum ambiguity angle of 30 degrees in the horizontal plane for a centered listener

Exploring the use of speech in audiology: A mixed methods study

This thesis aims to advance the understanding of how speech testing is, and can be, used for hearing device users within the audiological test battery. To address this, I engaged with clinicians and patients to understand the current role that speech testing plays in audiological testing in the UK, and developed a new listening test, which combined speech testing with localisation judgments in a dual task design. Normal hearing listeners and hearing aid users were tested, and a series of technical measurements were made to understand how advanced hearing aid settings might determine task performance. A questionnaire was completed by public and private sector hearing healthcare professionals in the UK to explore the use of speech testing. Overall, results revealed this assessment tool was underutilised by UK clinicians, but there was a significantly greater use in the private sector. Through a focus group and semi structured interviews with hearing aid users I identified a mismatch between their common listening difficulties and the assessment tools used in audiology and highlighted a lack of deaf awareness in UK adult audiology. The Spatial Speech in Noise Test (SSiN) is a dual task paradigm to simultaneously assess relative localisation and word identification performance. Testing on normal hearing listeners to investigate the impact of the dual task design found the SSiN to increase cognitive load and therefore better reflect challenging listening situations. A comparison of relative localisation and word identification performance showed that hearing aid users benefitted less from spatially separating speech and noise in the SSiN than normal hearing listeners. To investigate how the SSiN could be used to assess advanced hearing aid features, a subset of hearing aid users were fitted with the same hearing aid type and completed the SSiN once with adaptive directionality and once with omnidirectionality. The SSiN results differed between conditions but a larger sample size is needed to confirm these effects. Hearing aid technical measurements were used to quantify how hearing aid output changed in response to the SSiN paradigm