Physical Sound Source Research Articles

Categorization of Typical and Atypical Combinations of Excitations and Resonators of Musical Instruments: Assimilation of the Unusual to the Familiar

Sound categorization is automatic, yet very little is known about how this process works. Physical sound sources such as musical instruments generate sounds that carry timbral information about two mechanical components: The excitation sets into vibration the resonator, which acts as a filter to amplify, suppress, and radiate sound components. Given that excitation–resonator interactions are quite limited in the physical world, Modalys, a digital, physically inspired modeling platform, was utilized to simulate the combinations of three excitations (bowing, blowing, striking) and three resonators (string, air column, plate). This formed nine types of interactions, which are either typical (e.g., struck string) or atypical (e.g., blown plate). In two separate categorization tasks, participants chose either the excitation or resonator they thought produced each interaction. For the typical interactions, participants accurately categorized their excitations and resonators. Atypical interactions were assimilated to typical ones and listeners identified either the correct excitation or the correct resonator but not both. Hierarchical clustering revealed that interactions were perceived differently depending on the categorization task. These findings suggest that unfamiliar sound sources are interpreted as conforming to familiar sound sources for which mental models exist. These studies consequently exemplify the role of timbre in sound source recognition.

Influence of background noise on spatial audio localization for helicopter pilot headsets

A helicopter pilot is subjected to high workloads. A high noise level in the cockpit further increases stress. This stress can be reduced through headsets for hearing protection including active noise control (ANC). An actual research topic is the improvement of the human-machine-interface by 3-D-audio systems. These systems can improve pilot’s situational awareness and, therefore, reduce stress. This paper presents a 3-D-audio system for headphones. This binaural system uses head-tracking to process spatial information about the location of the sound source. The spatial sensation is achieved by convolving the source signal with head-related transfer functions. This sensation is influenced by background noise, which can be reduced by ANC. A first listening test with physical sound sources provides information on the localizability of sound sources at different elevation angles. This is compared to a second listening test with virtual sound sources generated by the 3-D-audio system. In a third listening test, the virtual sound source is located at variable azimuth and elevation angles. The system is evaluated with respect to sound source localization and the influence of background noise and ANC. This study highlights the potential of the 3-D-audio system to improve the helicopter pilot’s situational awareness in spatial acoustic environments.

The Effect of Auditory Residual Inhibition on Tinnitus and the Electroencephalogram.

Tinnitus is the perception of sound in the absence of an external physical sound source, for some people it can severely reduce the quality of life. Acoustic residual inhibition (ARI) is a suppression of tinnitus following the cessation of a sound. The present study investigated the effect of ARI on brain activity measured using EEG. Thirty adult participants (mean age of 58 years) experiencing chronic tinnitus (minimum 2 years) participated. Participants were presented broad band noise at 10 dB above minimum masking level (1 min followed by 4 min of silence, 4 times) counterbalanced with a control treatment of broad band noise at threshold (1 min followed by 4 min of silence, 4 times) while 64-channel EEG was simultaneously recorded. Tinnitus loudness was measured using a 9-point tinnitus loudness rating scale. The ARI stimulation resulted in a self-reported reduction in tinnitus loudness in 17 of the 30 participants. Tinnitus rating reduced following stimulation but gradually returned to near baseline during 4 min of silence post sound exposure; successive sound exposures resulted in lower loudness ratings. No significant reductions in loudness rating were found with the control stimulation. The EEG showed increases in power spectral density, particularly in the alpha and gamma bands, during ARI compared to the control periods. These results contribute to the understanding of ARI and tinnitus. We recommend that there be a closer examination of the relationship between onset and offset of sound in both tinnitus and nontinnitus control participants to ascertain if EEG changes seen with ARI relate to tinnitus suppression or general postsound activity.

Underwater Sound Sources and Ambient Noise in Fowlers Bay, South Australia, during the Austral Winter

Passive acoustic recordings made in Fowlers Bay, South Australia, during the austral winter of 2013–2017 revealed the presence of several sources of underwater sound. Sound sources of biological origin include baleen and toothed whales, fish and shrimp. Physical sources of underwater sound include wind- and rain-driven noises, and underwater sounds of anthropogenic origin were primarily from boats and occasionally from an aircraft. Biological sound sources were commonly recorded within the frequency range of around 25 Hz to nearly 17 kHz, with baleen whales within the range of ~ 25 Hz to 6 kHz, and dolphins at higher frequencies of approximately 2.5–17 kHz. Broadband sounds from physical and anthropogenic sound sources were noticeable at frequencies above ~ 50 Hz. The ambient noise level in Fowlers Bay at frequencies below 100 Hz was relatively low (around 75 dB re 1 µPa2/Hz for the 95% percentile) due to an insignificant contribution of noise from distant shipping. At higher frequencies, the noise level was governed primarily by noise from wind and varied by nearly 30 dB re 1 µPa2/Hz depending on weather conditions, up to around 80 dB re 1 µPa2/Hz for the 95% percentile during periods of strong winds and intense rainfall.

Tinnitus Management in Lateral Skull Base Lesions.

Tinnitus, the phantom perception of sound in the absence of a physical sound source, is a complex problem with multiple etiologies. While most commonly presenting in a subjective fashion caused by measurable hearing loss, other etiologies including lateral skull base tumors that encroach on middle and inner ear structures can lead to phantom sound perception as well. In addition to discussing the basic background of tinnitus, here we also review current theories of etiology that include central auditory and nonauditory neural mechanisms and potential treatments that range from sound therapy to medications to cognitive and behavioral therapies and cranial nerve and brain stimulation. One main purpose of this article is to relate tinnitus causes to skull base tumors, surgical removal, and resultant sequelae, including damage to cranial nerves resulting in audiovestibular dysfunction. We also discuss the utility of microvascular decompression for both tumor and nontumor-associated tinnitus and the current literature regarding hearing preservation rates and tinnitus perception, where documented, with the three common treatment modalities employed for most lateral skull base tumors that includes watchful waiting with serial imaging, stereotactic radiosurgery and primary surgical resection using hearing preservation and hearing ablative approaches. The management of skull base tumors is a complex process that depending upon the approach and sequelae, may lead to manageable or worsening phantom sound perception that must be considered when discussing the multiple treatment options with patients.

Interactions between front-back confusion and visual capture in summing localization

Ambiguity in binaural timing and level information often causes front-back confusions in sound localization. This experiment investigated the extent to which front-back confusions are modulated by concurrent visual stimuli. 15-ms duration noise stimuli were presented over two loudspeakers positioned at ±45o in front or behind a listener with a delay between them of −1—1 ms in steps of 0.5 ms, thus evoking summing localization. These sound stimuli were presented with or without light-flash stimuli at three different frontal locations. In comparison to audio only trials, when visual stimuli were also presented front-back confusion decreased for sound stimuli presented in front and increased for rear-presented auditory stimuli. This effect was greater for phantom sound sources than single speaker controls. These results suggest that visual cues influence the perceived location of a sound source when it is outside the field of vision. Further, the phantom sound sources presented using “summing localization” may offer less robust localization cues than physical sound sources, resulting in greater front-back confusion and stronger visual capture. Acoustic analyses of binaural and spectral cues are conducted to identify potential causes of the differences in FBC rates between single speaker and phantom sound sources.

The neural correlates of cognitive dysfunction in phantom sounds

Tinnitus is an auditory phantom percept with a tone, hissing or buzzing sound in the absence of an objective physical sound source. It has been shown that tinnitus can lead to emotional and cognitive impairment and people with tinnitus perform worse than a control group on different cognitive tasks. The hippocampus is known to play an important role in cognitive performance, and also in the pathophysiology of tinnitus. Hippocampal deficits have been described in animal models of tinnitus and in tinnitus patients a decrease in grey matter in the hippocampus has been demonstrated. Nineteen patients with tinnitus and fifteen healthy controls performed different cognitive processing tasks and underwent an EEG with source analysis to investigate the relationship between tinnitus loudness, tinnitus distress and tinnitus duration, cognitive impairment and neurophysiological changes in the hippocampus. Results show that both tinnitus loudness, tinnitus distress and tinnitus duration correlated positively with different cognitive measures (trail making test, Montreal cognitive assessment, mini mental state examination). It was also shown that these cognitive measures correlate with beta activity in the hippocampus, the pregenual and subgenual anterior cingulate cortex extending into the right insula. A region of interest analysis further confirms that beta activity in the left and right hippocampal area correlated with the trail making performance. In conclusion, these results support for the first time the notion that cognitive changes in tinnitus patients are associated with changes in hippocampal activity as well as the anterior cingulate and insula.

Natural Listening over Headphones in Augmented Reality Using Adaptive Filtering Techniques

Augmented reality (AR), which composes of virtual and real world environments, is becoming one of the major topics of research interest due to the advent of wearable devices. Today, AR is commonly used as assistive display to enhance the perception of reality in education, gaming, navigation, sports, entertainment, simulators, etc. However, most of the past works have mainly concentrated on the visual aspects of AR. Auditory events are one of the essential components in human perceptions in daily life but the augmented reality solutions have been lacking in this regard till now compared to visual aspects. Therefore, there is a need of natural listening in AR systems to give a holistic experience to the user. A new headphones configuration is presented in this work with two pairs of binaural microphones attached to headphones (one internal and one external microphone on each side). This paper focuses on enabling natural listening using open headphones employing adaptive filtering techniques to equalize the headset such that virtual sources are perceived as close as possible to sounds emanating from the physical sources. This would also require a superposition of virtual sources with the physical sound sources, as well as ambience. Modified versions of the filtered-x normalized least mean square algorithm (FxNLMS) are proposed in the paper to converge faster to the optimum solution as compared to the conventional FxNLMS. Measurements are carried out with open structure type headphones to evaluate their performance. Subjective test was conducted using individualized binaural room impulse responses (BRIRs) to evaluate the perceptual similarity between real and virtual sounds.

Multisensory attention training for treatment of tinnitus.

Tinnitus is the conscious perception of sound with no physical sound source. Some models of tinnitus pathophysiology suggest that networks associated with attention, memory, distress and multisensory experience are involved in tinnitus perception. The aim of this study was to evaluate whether a multisensory attention training paradigm which used audio, visual, and somatosensory stimulation would reduce tinnitus. Eighteen participants with predominantly unilateral chronic tinnitus were randomized between two groups receiving 20 daily sessions of either integration (attempting to reduce salience to tinnitus by binding with multisensory stimuli) or attention diversion (multisensory stimuli opposite side to tinnitus) training. The training resulted in small but statistically significant reductions in Tinnitus Functional Index and Tinnitus Severity Numeric Scale scores and improved attentional abilities. No statistically significant improvements in tinnitus were found between the training groups. This study demonstrated that a short period of multisensory attention training reduced unilateral tinnitus, but directing attention toward or away from the tinnitus side did not differentiate this effect.

The auditory cortex and tinnitus – a review of animal and human studies.

Tinnitus is the sound heard in the absence of physical sound sources external or internal to the body. Tinnitus never occurs in isolation; it typically develops after hearing loss, and not infrequently for losses at the higher frequencies not tested in clinical audiology. Furthermore, tinnitus is often accompanied by hyperacusis, i.e. increased loudness sensitivity, which may reflect the central gain change in the auditory system that occurs after hearing loss. I will first review the electrophysiological findings in the thalamus and cortex pertaining to animal research into tinnitus. This will comprise the changes in tonotopic maps, spontaneous firing rates and changes in pairwise neural cross-correlation induced by tinnitus-inducing agents that are commonly used in animal experiments. These are systemic application of sodium salicylate, and noise exposure at levels ranging from those that do not cause a hearing loss, to those that only cause a temporary threshold shift, to those that cause a permanent hearing loss. Following this, I will review neuroimaging and electrophysiological findings in the auditory cortex in humans with tinnitus. The neural substrates of tinnitus derived from animal data do not apply universally, as neither hearing loss nor hyperacusis appear to be necessary conditions for tinnitus to occur in humans. Finally, I will relate the findings in humans to the predictions from animal models of tinnitus. These comparisons indicate that neural correlates of tinnitus can be studied successfully both at the level of animal models and in humans.

Maladaptive neural synchrony in tinnitus: origin and restoration.

Tinnitus is the conscious perception of sound heard in the absence of physical sound sources external or internal to the body, reflected in aberrant neural synchrony of spontaneous or resting-state brain activity. Neural synchrony is generated by the nearly simultaneous firing of individual neurons, of the synchronization of membrane-potential changes in local neural groups as reflected in the local field potentials, resulting in the presence of oscillatory brain waves in the EEG. Noise-induced hearing loss, often resulting in tinnitus, causes a reorganization of the tonotopic map in auditory cortex and increased spontaneous firing rates and neural synchrony. Spontaneous brain rhythms rely on neural synchrony. Abnormal neural synchrony in tinnitus appears to be confined to specific frequency bands of brain rhythms. Increases in delta-band activity are generated by deafferented/deprived neuronal networks resulting from hearing loss. Coordinated reset (CR) stimulation was developed in order to specifically counteract such abnormal neuronal synchrony by desynchronization. The goal of acoustic CR neuromodulation is to desynchronize tinnitus-related abnormal delta-band oscillations. CR neuromodulation does not require permanent stimulus delivery in order to achieve long-lasting desynchronization or even a full-blown anti-kindling but may have cumulative effects, i.e., the effect of different CR epochs separated by pauses may accumulate. Unlike other approaches, acoustic CR neuromodulation does not intend to reduce tinnitus-related neuronal activity by employing lateral inhibition. The potential efficacy of acoustic CR modulation was shown in a clinical proof of concept trial, where effects achieved in 12 weeks of treatment delivered 4–6 h/day persisted through a preplanned 4-week therapy pause and showed sustained long-term effects after 10 months of therapy, leading to 75% responders.

A study on large coherent structures and noise emission in a turbulent round jet

A moderate Reynolds number, and high subsonic turbulent round jet is investigated by large eddy simulation. The detailed results (e.g. mean flow properties, turbulence intensities, etc.) are validated against the experimental data, and special attention is paid to study motions of coherent structures and their contributions to far-field noise. Eulerian methods (e.g. Q-criteria and λ2 criteria) are utilized for visualizing coherent structures directly for instantaneous flow fields, and Lagrangian coherent structures accounting for integral effect are shown via calculating fields of finite time Lyapunov exponents based on bidimensional velocity fields. All visualizations demonstrate that intrusion of three-dimensional vortical structures into jet core occurs intermittently at the end of the potential core, resulting from the breakdown of helical vortex rings in the shear layer. Intermittencies in the shear layer and on the centerline are studied quantitatively, and distinctively different distributions of probability density function are observed. Moreover, the physical sound sources are obtained through a filtering operation of defined sources in Lighthill’s analogy, and their distributions verify that intrusion of vortical structures into the core region serves as important sound sources, in particular for noise at aft angles. The facts that intermittent behaviors are caused by motions of coherent structures and correlated with noise generation imply that to establish reasonable sound sources in active noise production region based on intermittent coherent structures is one of the key issues for far-field noise prediction.

Temporally diffusive reflections and the precedence effect

In reverberant conditions, humans routinely demonstrate an ability to form the auditory event in the direction of the first wavefront and thus identify the direction of the (physical) sound source—the so-called “Precedence Effect.” Within limits, this effect even holds when the reflected sounds (the lag) contain more energy than the direct sound (the lead). Previously, we investigated the lateral extent of the Precedence Effect for specular reflections. The current research extends this inquiry by investigating the effect of temporally diffusive reflections, using the same stimuli, but convolving the lag with a 2-ms Hanning windowed Gaussian noise. The lead and lag stimuli were 200-ms Gaussian noise (500-Hz center frequency, 800-Hz bandwidth) presented dichotically with a programmable amount of temporal overlap. The lag/lead level ratio was increased in 2-dB steps, the lead/lag interval was varied from −5 to 5-ms in steps of 1-ms. Listeners indicated the lateralization of their auditory events with an acoustic pointer. The resulting temporal smearing substantially decorrelates lead and lag while keeping them essentially related. The Precedence Effect is found to be more robust to increases of the lag level for diffusive stimuli than for the previously tested sets of specular reflections.

Comparing immediate transient tinnitus suppression using tACS and tDCS: a placebo-controlled study

Tinnitus is an auditory phantom percept with a tone, hissing, or buzzing sound in the absence of any objective physical sound source. Two forms of low-intensity cranial electrical stimulation exist for clinical and research purposes: transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS). In a recent study, it was demonstrated that a single session of tDCS over the dorsolateral prefrontal cortex (DLPFC) (anode over right DLPFC) yields a transient improvement in subjects with chronic tinnitus and that repeated sessions can possibly be used as a treatment. In the present study, the effect of a single-session individual alpha-modulated tACS and tDCS applied at the DLPFC bilaterally is compared with tinnitus loudness and tinnitus annoyance. A total of fifty tinnitus patients were selected and randomly assigned to the tACS or tDCS treatment. Our main result was that bifrontal tDCS modulates tinnitus annoyance and tinnitus loudness, whereas individual alpha-modulated tACS does not yield a similar result. This study provides additional insights into the role of DLPFC in tinnitus modulation as well as the intersection between tinnitus and affective/attentional processing.

The involvement of the left ventrolateral prefrontal cortex in tinnitus: a TMS study

Tinnitus is an auditory phantom percept with a tone, hissing or buzzing sound in the absence of any objective physical sound source. Tinnitus is considered to be an auditory phantom phenomenon analogous to somatosensory phantom pain. Controllable versus uncontrollable pain is characterized by an increased activity in the ventrolateral prefrontal cortex (VLPFC), and activation in the VLPFC correlating with perceived control over pain results in a decrease in subjective pain intensity. Depressed individuals show less activation than healthy controls in the left VLPFC in response to sad autobiographical scripts, and greater relative left prefrontal activation is related to a greater disposition to approach-related, positive affect with a greater ability to regulate negative affect. Based on the theory that non-pulsatile tinnitus can be considered the auditory analogue for deafferentation pain, we hypothesize that the left VLPFC might also be involved in control of tinnitus. We conducted a transcranial magnetic stimulation (TMS) study verifying whether modulating the left VLPFC by TMS can modulate the loudness of tinnitus. We studied 60 patients with chronic tinnitus of which 21 patients received in random order sham and 1-Hz stimulation, while 39 patients received in random order sham and 10-Hz stimulation. Our results show that 10-Hz stimulation can modulate tinnitus loudness, while 1-Hz stimulation does not seem to exert the same effect. Our findings give further support to the fact that non-auditory areas are involved in tinnitus.

EEG Driven tDCS Versus Bifrontal tDCS for Tinnitus

Tinnitus is the perception of a sound in the absence of any objective physical sound source. Transcranial Direct Current Stimulation (tDCS) induces shifts in membrane resting potentials depending on the polarity of the stimulation: under the anode gamma band activity increases, whereas under the cathode the opposite occurs. Both single and multiple sessions of tDCS over the dorsolateral prefrontal cortex (DLPFC; anode over right DLPFC) yield a transient improvement in tinnitus intensity and tinnitus distress. The question arises whether optimization of the tDCS protocol can be obtained by using EEG driven decisions on where to place anode and cathode. Using gamma band functional connectivity could be superior to gamma band activity as functional connectivity determines the tinnitus network in many aspects of chronic tinnitus. Six-hundred-seventy-five patients were included in the study: 265 patients received tDCS with cathodal electrode placed over the left DLPFC and the anode placed overlying the right DLPFC, 380 patients received tDCS based on EEG connectivity, and 65 received no tDCS (i.e., waiting list control group). Repeated measures ANOVA revealed a significant main effect for pre versus post measurement. Bifrontal tDCS in comparison to EEG driven tDCS had a larger reduction for both tinnitus distress and tinnitus intensity. Whereas the results of the bifrontal tDCS seem to confirm previous studies, the use of gamma band functional connectivity seems not to bring any advantage to tDCS for tinnitus suppression. Using other potential biomarkers, such as gamma band activity, or theta functional connectivity could theoretically be of use. Further studies will have to elucidate whether brain state based tDCS has any advantages over “blind” bifrontal stimulation.

The Use of Alcohol as a Moderator for Tinnitus-Related Distress

Tinnitus is an auditory phantom percept with a tone, hissing, or buzzing sound in the absence of any objective physical sound source. Persons with tinnitus engage in a number of health behaviors to manage tinnitus. This can go from prescription medication, masking devices, behavioral training techniques to cortical implants. Potentially less adaptive methods of coping with tinnitus, such as the use of alcohol, are poorly studied. The purpose of this study was to further explore the neurobiological mechanism of tinnitus improvement by the use of alcohol. We observed differences in the alpha, beta and gamma frequency band when comparing resting-state EEG before and after alcohol intake. More precisely increased synchronized alpha1 activity was found in the posterior cingulate cortex and decreased synchronized alpha2 activity was demonstrated in orbitofrontal cortex, ventrolateral prefrontal cortex and subcallosal anterior cingulate cortex after alcohol intake. Increased synchronized activity was found in a region between the pregenual and dorsal anterior cingulate cortex and the left insula for beta and decreased activity in the precuneus after alcohol intake. For the gamma frequency band decreased synchronized activity in the precuneus and the posterior cingulate cortex was demonstrated after alcohol intake. Region of interest analyses in auditory cortices and parahippocampal area revealed however no differences in the different frequency bands before and after alcohol consumption.

Numerical Comparison of Different Equivalent Source Models and Source Quantification Techniques for Use in Sound Synthesis Systems

The aim of sound synthesis methods is to auralize the sound of a physical sound source in the way it is perceived by a listener at a particular location. Most existing synthesis methods start with a source - transmission path -receiver (s-t-r) model to predict spectral characteristics of the sound at the receiver location (e.g. a time-frequency spectrum). To define such a s-t-r model, an adequate representation of the physical sound source is crucial for achieving high quality sound syntheses. In the mid-frequency range, equivalent source models composed of a limited number of elementary substitute sources are usually applied. These equivalent models overcome many of the disadvantages of other sound source reconstruction models. However, quantification of the elementary substitute sources is difficult. After propagation along the transmission path and based upon the predicted spectral characteristics, the sound synthesis methods then synthesize an audible sound at the receiver location. This paper presents a numerical study on the performance of different equivalent source models and quantification techniques. It is shown that the recently developed inverse quantification approach based on acoustic particle velocities can be a fast and sufficient accurate alternative for techniques based on velocity and acceleration on the source surface or on acoustic pressures at indicator positions around the source. Furthermore, guidelines are given to select the number of equivalent substitute sources.

Temporal coherence and attention in auditory scene analysis

Humans and other animals can attend to one of multiple sounds and follow it selectively over time. The neural underpinnings of this perceptual feat remain mysterious. Some studies have concluded that sounds are heard as separate streams when they activate well-separated populations of central auditory neurons, and that this process is largely pre-attentive. Here, we argue instead that stream formation depends primarily on temporal coherence between responses that encode various features of a sound source. Furthermore, we postulate that only when attention is directed towards a particular feature (e.g. pitch) do all other temporally coherent features of that source (e.g. timbre and location) become bound together as a stream that is segregated from the incoherent features of other sources.

The neural correlates of tinnitus-related distress

Tinnitus is an auditory phantom percept with a tone, hissing, or buzzing sound in the absence of any objective physical sound source. About 6% to 25% of the affected people report interference with their lives as tinnitus causes a considerable amount of distress. However, the underlying neurophysiological mechanism for the development of tinnitus-related distress remains not well understood. Hence we focus on the cortical and subcortical source differences in resting-state EEG between tinnitus patients with different grades of distress using continuous scalp EEG recordings and Low Resolution Electromagnetic Tomography (LORETA). Results show more synchronized alpha activity in the tinnitus patients with a serious amount of distress with peaks localized to various emotion-related areas. These areas include subcallosal anterior cingulate cortex, the insula, parahippocampal area and amygdala. In addition, less alpha synchronized activity was found in the posterior cingulate cortex, precuneus and DLPFC. A comparison between the tinnitus group with distress and the Nova Tech EEG (NTE) normative database demonstrated increased synchronized alpha and beta activity and less synchronized delta and theta activity in the dorsal anterior cingulate cortex in tinnitus patients with distress. It is interesting that the areas found show some overlap with the emotional component of the pain matrix and the distress related areas in asthmatic dyspnea. Unpleasantness of pain activates the anterior cingulate and prefrontal cortices, amygdala, and insula. As such, it might be that distress is related to alpha and beta activity in the dorsal anterior cingulate cortex, the amount of distress perceived to an alpha network consisting of the amygdala-anterior cingulate cortex-insula–parahippocampal area.