Examensarbete om binaurala ljud och om manipulering av monoljud kan efterlikna binaurala ljud.

Cochlear implants provide hearing to people who are deaf, by electrically stimulating the auditory nerve. Children with a single cochlear implant suffer deficiencies inherent to unilateral hearing, including inability to locate sounds. A second cochlear implant may improve sound localization, which normally requires interpretation of differences in sound intensity and time of arrival between two ears. Currently, it is unknown whether these cues are available to children who were provided with a second cochlear implant after a period of using one implant alone. We asked whether such children could interpret inter-implant level and timing cues. Results indicated that children using two cochlear implants detected level cues but had difficulty interpreting timing cues. Further, children rarely reported that sounds were perceived to come from the middle. Children receiving bilateral cochlear implants sequentially do not process bilateral auditory cues normally but can use inter-implant level cues to make judgments about where sound is coming from.

Cochlear implants provide hearing to people who are deaf, by electrically stimulating the auditory nerve. Children with a single cochlear implant suffer deficiencies inherent to unilateral hearing, including inability to locate sounds. A second cochlear implant may improve sound localization, which normally requires interpretation of differences in sound intensity and time of arrival between two ears. Currently, it is unknown whether these cues are available to children who were provided with a second cochlear implant after a period of using one implant alone. We asked whether such children could interpret inter-implant level and timing cues. Results indicated that children using two cochlear implants detected level cues but had difficulty interpreting timing cues. Further, children rarely reported that sounds were perceived to come from the middle. Children receiving bilateral cochlear implants sequentially do not process bilateral auditory cues normally but can use inter-implant level cues to make judgments about where sound is coming from.

While most of today’s music listening is being done through headphones, mixing techniques using binaural audio are still not widely implemented in modern music production. This study aims to help inform mixing engineers on the applicability of binaural processing for music production, with the specific focus on how binaurally processed audio translates to loudspeakers in terms of listener preference. In this study a listening test was performed where binaurally processed mixes where given preference ratings in relation to a reference mix. Each listener completed the test twice, once using headphones and once using loudspeakers. The test results for the two playback systems were then compared. Only one of 12 mixes showed a significant difference in preference ratings with playback system as the factor, but the reported ratings showed a large disagreement among the 13 test subjects. The results from the study are inconclusive, however they do not suggest that the binaural processing used for the stimuli suffers in terms of listener preference when played back over loudspeakers.

Although a majority of the listening is done on headphones today, most, if not all, televised arena sports is still mixed for loudspeakers. By providing binaural audio for headphones listening, the qualities of surround sound could potentially be experienced on headphones. To find out if this holds true, 13 subjects with experience of critical listening agreed to perform a listening test where they were asked to rate four attributes of which preference is one. To the rating of preference, they also had to argue for their thinking. Lastly, further attributes and qualities was collected to find what attributes seem to be of greatest importance for rating of arena sports in binaural. The results show no statistical significance when comparing the ratings of the binaural and stereo mix for each attribute, and the sample group is clearly disagreeing what stimuli to rate the highest. The collection of qualitative data gave better results and could be summarized to seven attributes of which four appeared in the data from more than half of the test subject. With this result it is clear that more research is needed to find what the most important aspects of binaural mixing are, and how binaural audio best can be used for televised arena sports.

Speech enhancement in multi-speaker babble remains an enormous challenge. In this study, we developed a binaural speech enhancement system to extract information pertaining to a target speech signal embedded in a noisy background for use in future hearing-aid systems. The principle underlying the proposed system is to simulate the perceptual auditory segregation process carried out in the normal human auditory system. Based on the spatial location, pitch and onset cues, the system can identify and enhance those time-frequency regions which constitute the target speech. The proposed system is capable of dealing with a wide variety of noise intrusions, including competing speech signals and multi-speaker babble. It also works under mild reverberation conditions. Systematic evaluation shows that the system achieves substantial improvement on the intelligibility of target signal, while it largely suppresses the unwanted background signal. / Thesis / Master of Applied Science (MASc)

The brain is a highly complex network of nonlinear systems with internal dynamic states that are not easily quantified. As a result, it is essential to understand the properties of the connectivity network linking disparate parts of the brain used in complex cognitive processes, such as working memory. Working memory is the system in control of temporary retention and online organization of thoughts for successful goal directed behavior. Individuals exhibit a typically small capacity limit on the number of items that can be simultaneously retained in working memory. To modify network connections and thereby augment working memory capacity, researchers have targeted brain areas using a variety of noninvasive stimulation interventions. However, few existing methods take advantage of the brain's own structure to actively generate and entrain internal oscillatory modulations in locations deep within the auditory pathways. One technique is known as binaural beats, which arises from the brain's interpretation of two pure tones, with a small frequency mismatch, delivered independently to each ear. The mismatch between these tones is perceived as a so-called beat frequency which can be used to modulate behavioral performance and cortical connectivity. Currently, all binaural stimulation therapeutic systems are open-loop "one-size-fits-all" approaches. However, these methods can prove not as effective because each person's brain responds slightly differently to exogenous stimuli. Therefore, the driving motivation for developing a closed-loop stimulation system is to help populations with large individual variability. One such example is persons with mild cognitive impairment (MCI), which causes cognitive impairments beyond those expected based on age. Therefore, applying a closed-loop binaural beat control system to increase the cognitive load level to people with MCI could potentially maintain their quality of life. In this dissertation, I will present a comparison of algorithms to determine brain connectivity, results of open-loop based binaural stimulation, the development of a closed-loop brain network simulation platform, and finally an experimental study to determine the effectiveness of closed-loop control to modulate brain networks hence influencing cognitive abilities. / Ph. D. / In order to do complex tasks, such as creating a memory, multiple regions of the brain must interact to become a network. Specifically for this work, we are looking at working memory which is the system that allows us to remember and manipulate information in the presence of additional incoming information. Working memory capacity, which is the number of items we can remember, is dependent upon synchronization between particular regions of the brain, particularly the frontal and parietal lobes. Higher synchronization means that people will, on average, respond with higher accuracy during a working memory task. To modify the connections in the network and thereby augment working memory capacity, a non-invasive brain stimulation technique called binaural beats can be used. Binaural beats take advantage of the brain’s response to two pure tones, delivered independently to each ear, when those tones have a small frequency mismatch. The mismatch between the tones is interpreted as a beat frequency, which may act to synchronize brain waves. This research seeks to answer the question of whether binaural beats can be used to identify and control working memory. Currently, nearly all therapeutic stimulation systems are open-loop “one-size-fits-all” approaches. However, these methods can prove not as effective because each person’s brain responds slightly differently to external stimuli. Therefore, the driving motivation for developing a closed-loop stimulation system is to help populations with large individual variability. One such example is persons with mild cognitive impairment (MCI) which is considered a precursor to Alzheimer’s. Therefore, applying a closed-loop binaural beat control system to increase the cognitive load level to people with MCI could potentially maintain their quality of life. In this dissertation, we have showed that we can successfully increase the connectivity in the brain using binaural beats in a closed-loop system.

The purpose of the study was to determine whether hearing aids with binaural processing improve performance during a localization and a hearing in noise task. The study included 16 participants, ages 29 – 67, with bilateral, essentially symmetrical, sensorineural hearing loss who had no prior hearing aid experience. Participants were fit with Oticon Epoq XW hearing aids bilaterally and completed the localization and the hearing in noise task with three listening conditions: (1) without hearing aids (NO), (2) with hearing aids that were not linked (BIL), and (3) with hearing aids that were linked (BIN). For the localization task, 1.5 second pink noise bursts at 75 dB SPL were used as the stimulus. A 180° 11-speaker array was set up to the right or left side of the participants. A twelfth speaker on the contralateral side of the array introduced constant background pink noise at 65 dB SPL. Results revealed that participants performed the best with the NO condition, followed by BIL, then BIN. There was a significant difference between NO and BIL and NO and BIN. For the hearing in noise (HIN) task, sentences from the Hearing in Noise Test (HINT) were used as target stimuli. Continuous discourse by one male and two female talkers were used as maskers. There were four masker conditions for this task: (1) signal at 0°, masker at 90° (S0-N90), (2) signal at 0°, masker at 180° (S0-N180), (3) signal at 0°, masker at 270° (S0-N270), and (4) signal at 0°, maskers at 90°, 180°, and 270° (S0-N90, 180, 270). Results revealed that there was no significant difference between listening conditions when all masker conditions were considered. When the one-masker conditions were included, there was a significant difference between the NO and BIL and the NO and BIN conditions with the best performance for BIL, followed by BIN, then NO. Results also revealed a significant difference between masker conditions with the best performance for S0-N270, next best for S0-N90, followed by S0-N180, then S0-N90, 180, 270. / text

The main focus of the research presented within this thesis is, as the title suggests, binaural spatialization. Binaural technology and, especially, the binaural recording technique are not particu-larly recent. Nevertheless, the interest in this technology has lately become substantial due to the increase in the calculation power of personal computers, which started to allow the complete and accurate real-time simulation of three-dimensional sound-fields over headphones. The goals of this body of research have been determined in order to provide elements of novelty and of contribution to the state of the art in the field of binaural spatialization. A brief summary of these is found in the following list: • The development and implementation of a binaural spatialization technique with Distance Simulation, based on the individual simulation of the distance cues and Binaural Reverb, in turn based on the weighted mix between the signals convolved with the different HRIR and BRIR sets; • The development and implementation of a characterization process for modifying a BRIR set in order to simulate different environments with different characteristics in terms of frequency response and reverb time; • The creation of a real-time and offline binaural spatialization application, imple-menting the techniques cited in the previous points, and including a set of multichannel(and Ambisonics)-to-binaural conversion tools. • The performance of a perceptual evaluation stage to verify the effectiveness, realism, and quality of the techniques developed, and • The application and use of the developed tools within both scientific and artistic “case studies”. In the following chapters, sections, and subsections, the research performed between January 2006 and March 2010 will be described, outlining the different stages before, during, and after the development of the software platform, analysing the results of the perceptual evaluations and drawing conclusions that could, in the future, be considered the starting point for new and innovative research projects.

<p>Studien riktar sig främst till audionomer, och andra med intresse av hörselrehabilitering.</p><p>Auditiv deprivering kan visa sig som en med tiden försämrad taluppfattning i örat som inte fått adekvat stimulering. Vad som karaktäriserar dem som drabbas är inte klarlagt. Inte heller vet man exakt orsak eller tidsförlopp. Genom att hörapparatanpassa det drabbade örat har effekten kunnat reduceras och i vissa fall har fullständig återhämtning konstaterats.</p><p>Litteraturstudiens syfte var att belysa fenomenet och aspekter som bör beaktas i audionomens arbete med insatser av både förebyggande och rehabiliterande karaktär. Metoden var att granska artiklar framtagna genom systematisk och manuell sökning, i databaser tillgängliga genom Örebro universi¬tet.</p><p>Resultatet visar att personer med hörselnedsättning av såväl sensorineural som konduktiv art drabbas. Hörselnedsättningens grad kan troligen påverka, liksom symmetrin mellan öronen. Den initiala taluppfattningen i örat som drabbas kan variera. Detta arbete visar också att en sensitiv metod för att konstatera effekten är den som i Sverige heter maximal taluppfattning, men objektiva mätmetoder välkomnas. Audionomens ställningstagande i val av en eller två hörapparater berörs, med utgångspunkt av auditiv deprivering och binaural interference. Resultat och diskussion lyfter viktiga aspekter att beakta för audionomen i det rehabiliterande arbetet.</p>