Sound Masking Research Articles

Simulated masking of right whale sounds by shipping noise: Incorporating a model of the auditory periphery

Many species of large, mysticete whales are known to produce low-frequency communication sounds. These low-frequency sounds are susceptible to communication masking by shipping noise, which also tends to be low frequency in nature. The size of these species makes behavioral assessment of auditory capabilities in controlled, captive environments nearly impossible, and field-based playback experiments are expensive and necessarily limited in scope. Hence, it is desirable to produce a masking model for these species that can aid in determining the potential effects of shipping and other anthropogenic noises on these protected animals. The aim of this study was to build a model that combines a sophisticated representation of the auditory periphery with a spectrogram-based decision stage to predict masking levels. The output of this model can then be combined with a habitat-appropriate propagation model to calculate the potential effects of noise on communication range. For this study, the model was tested on three common North Atlantic right whale communication sounds, both to demonstrate the method and to probe how shipping noise affects the detection of sounds with varying spectral and temporal characteristics.

The Subcomponents of Informational Masking: Evidence from Behavioral and Neural Imaging Studies

The processing of a target speech under noisy environment is influenced by the presence of concurrent sounds, this phenomenon is referred to as auditory masking. Previous research showed that there are two kinds of masking, energetic masking and informational masking. Energetic masking originated from auditory periphery, where the masking sound overlaps with the target sound in time and frequency, resulting in an incomplete representation of the latter. On the other hand, informational masking is believed to occur in the central auditory system. However, for a long time, the concept of informational masking has been used as a "suitcase" or "catchall" word. All the influencing effect that can not be explained by energetic masking is attributed to informational masking, though its underlying mechanism is still largely unknown. In this article, a new conceptual framework of informational masking is proposed. In this framework, informational masking is divided into two subcomponents, perceptual informational masking and cognitive informational masking. Perceptual masking is caused by the competition between the sound stream/object, while cognitive informational masking is caused by the higher cognitive information included in the masking sounds, which could be automatically processed by the auditory or linguistic system. Psychophysical and neural imaging studies are proposed to test the above hypothesis. In behavioral studies, the perceived spatial separation between the target and the masker, the intelligibility and the voice number in the masking sound, as well as the perceptual similarity between the target and masker streams are manipulated to demonstrate that perceptual masking and cognitive masking could be double-dissociated. In the neural imaging study, fMRI technique is used to show that perceptual and cognitive informational masking may have different neural mechanism.

Efficiency of sound masking system for elderly people with degraded auditory properties

Efficiency of sound masking system for elderly people with degraded auditory properties

The do’s and don’ts of electronic sound masking

Electronic sound masking, when properly implemented, can be an effective tool for introducing background noise in occupied spaces, which is a key factor of speech privacy. Mechanical ventilation systems generally cannot be relied upon to provide the consistent and appropriate levels of background noise that sound masking systems are capable of, and this is even more the case with variable-air-volume systems and several emerging (or re-emerging) technologies such as natural ventilation, underfloor air distribution, and chilled beams. However, despite general industry consensus of what constitutes appropriate levels of background noise, striking discrepancies in acoustic performance have been observed for several recent sound masking installations, thus defeating the original objectives for such a system. Fortunately, such issues can be avoided if design efforts account for limitations of both the sound masking system and acoustics of the space, clear performance requirements are established, and the system is properly adjusted and balanced prior to occupancy. Through case studies, this paper seeks through to illustrate the need for a guided approach toward achieving successful outcomes while also highlighting the broader range of issues involved with speech privacy.

Objective measures of binaural masking level differences and comodulation masking release based on late auditory evoked potentials

The audibility of important sounds is often hampered due to the presence of other masking sounds. The present study investigates if a correlate of the audibility of a tone masked by noise is found in late auditory evoked potentials measured from human listeners. The audibility of the target sound at a fixed physical intensity is varied by introducing auditory cues of (i) interaural target signal phase disparity and (ii) coherent masker level fluctuations in different frequency regions. In agreement with previous studies, psychoacoustical experiments showed that both stimulus manipulations result in a masking release (i: binaural masking level difference; ii: comodulation masking release) compared to a condition where those cues are not present. Late auditory evoked potentials (N1, P2) were recorded for the stimuli at a constant masker level, but different signal levels within the same set of listeners who participated in the psychoacoustical experiment. The data indicate differences in N1 and P2 between stimuli with and without interaural phase disparities. However, differences for stimuli with and without coherent masker modulation were only found for P2, i.e., only P2 is sensitive to the increase in audibility, irrespective of the cue that caused the masking release. The amplitude of P2 is consistent with the psychoacoustical finding of an addition of the masking releases when both cues are present. Even though it cannot be concluded where along the auditory pathway the audibility is represented, the P2 component of auditory evoked potentials is a candidate for an objective measure of audibility in the human auditory system.

Prediction of the Effectiveness of a Sound-Masking System in an Open-Plan Office Including the Lombard Effect

Sound masking can improve speech privacy in rooms by increasing background-noise levels that mask distracting speech sounds. The Lombard Effect indicates that an increase in background-noise level can increase talker voice levels, reducing speech privacy and the benefit of a sound-masking system. To investigate this, a model of an existing open-plan office was created in CATT-Acoustics and validated. The model was used to predict speech-transmission index (STI) and the effectiveness of a sound-masking system, without and with the Lombard Effect, described by the existing Lombard Voice Model. Predictions were made for ambient-noise levels of 30, 40, and 45 dBA, at various distances from a primary talker, and for 0–4 secondary talkers. With 30-dBA ambient noise, STIs at 1 and 4 m varied with the number of talkers from 0.67 to 0.91 and 0.23 to 0.62 without the sound-masking system, from 0.58 to 0.70 and 0.13 to 0.25 with it but ignoring the Lombard Effect, and from 0.64 to 0.73 and 0.18 to 0.27 with the Lombard Effect. The Lombard Effect reduced the benefit of the sound-masking system by 3–9% and 7–22%. With higher ambient noise, the system is less effective; the Lombard Effect can almost cancel its benefit, resulting in increased STI (decreased privacy) with the system operating.

Prediction of the effectiveness of a sound-masking system in an open-plan office including the Lombard Effect

Sound masking can improve speech privacy in rooms by increasing background-noise levels that mask distracting speech sounds. The Lombard Effect indicates that an increase in background-noise level can increase talker voice levels, reducing speech privacy and the benefit of a sound-masking system. To investigate this, a model of an existing open-plan office was created in CATT-Acoustics and validated. The model was used to predict speech-transmission index (STI) and the effectiveness of a sound-masking system, without and with the Lombard Effect, described by the existing Lombard Voice Model. Predictions were made for ambient-noise levels of 30, 40, and 45 dBA, at various distances from a primary talker, and for 0–4 secondary talkers. With 30-dBA ambient noise, STIs at 1 and 4 m varied with the number of talkers from 0.67 to 0.91 and 0.23 to 0.62 without the sound-masking system, from 0.58 to 0.70 and 0.13 to 0.25 with it but ignoring the Lombard Effect, and from 0.64 to 0.73 and 0.18 to 0.27 with the Lombard Effect. The Lombard Effect reduced the benefit of the sound-masking system by 3–9% and 7–22%. With higher ambient noise, the system is less effective; the Lombard Effect can almost cancel its benefit, resulting in increased STI (decreased privacy) with the system operating.

Work performance and mental workload in multiple talker environments

The impairment of cognitive performance resulting from the presence of speech sounds is known to increase as the intelligibility of the speech signals is improved. For that reason, speech intelligibility measures are used to quantify the nuisance potential of an unattended voice. However, most of these indexes struggle with situations in which the level of the masking sound is fluctuating. This is the case in open-plan offices, where competing voices are involved. This paper relates a set of experiments in which subjects had to carry out a basic memory task in various noise settings. In addition to a target speech, the masking sounds were made up of speech and differed in temporal variability. The signal-to-noise ratios and the overall long-term spectra were kept constant. Disturbance was assessed both through objective measurements of performance and subjective reports of workload. The results highlight the importance of taking into account the temporal fluctuations of the overall ambient sound when trying to ascertain the influence of speech intelligibility on observed and perceived disturbance during the performing of a mental activity. Insights are provided, which could lead to the use of a speech intelligibility measure better equipped to deal with multi-sources environments.

A consideration on sound masking system for achieving speech privacy using parametric acoustic array speaker

Speech privacy in open spaces is becoming increasingly important in various situations. Although measures such as the use of sound partitions are already used in many cases, measures that mask speech by emitting sounds have also been considered. A method of masking meaningful speech with meaningless noise would be valuable. Because of this, previous studies have investigated the ability of meaningless steady noise to mask speech and consequently achieve speech privacy. However, the research to date has focused on evaluating speech privacy when the masking noise is emitted from the normal loud speaker system all over the room. The masking noise emitted to the area where high level of speech privacy is not required, may cause an increased psychological impression of annoyance, leading to a decline in performance. In this study, we used a highly directional sound from modulated ultrasound as a masking noise for achieving speech privacy in the narrow area. Psychological experiments were conducted in which the masking sound was transmitted to participants from frontal or above directions with a parametric acoustic array speaker. Using the experimental data, the relationships between the degree of speech privacy and frequency characteristics and directivity of parametric acoustic array speaker were investigated. The results suggested that it is possible to maintain speech privacy in the narrow area by presenting highly directional masking sound.

Masking of sounds by a background noise – cochlear mechanical correlates

In the search for cochlear correlates of auditory masking by noise stimuli, we recorded basilar membrane (BM) vibrations evoked by either tone or click signals in the presence of varying levels of background noise. The BM vibrations were recorded from basal regions in healthy cochleae of anaesthetized chinchilla and gerbil. Non-linear interactions that could underpin various aspects of psychophysical masking data, including both compression and suppression at the BM level, were observed. The suppression effects, whereby the amplitude of the responses to each stimulus component could be reduced, depended on the relative intensities of the noise and the tones or clicks. Only stimulus components whose frequencies fell inside the non-linear region of the recording site, i.e. around its characteristic frequency (CF), were affected by presentation of the 'suppressing' stimulus (which could be either the tone or the noise). Mutual suppression, the simultaneous reduction of the responses to both tones and noise components, was observed under some conditions, but overall reductions of BM vibration were rarely observed. Moderate- to high-intensity tones suppressed BM responses to low-intensity Gaussian stimuli, including both broadband and narrowband noise. Suppression effects were larger for spectral components of the noise response that were closer to the CF. In this regime, the tone and noise stimuli became the suppressor and probe signals, respectively. This study provides the first detailed observations of cochlear mechanical correlates of the masking effects of noise. Mechanical detection thresholds for tone signals, which were arbitrarily defined using three criteria, are shown to increase in almost direct proportion to the noise level for low and moderately high noise levels, in a manner that resembles the findings of numerous psychophysical observations.

An Evaluation Framework for Environmentally Sustainable Development of the Historic Cities within the Context of City Squares in Isfahan-Iran

The urban development involves more sensitive challenges for evaluation of the urban land use in respect of the framework of sustainable development. In the last three decades, the concept of sustainable development has developed into a broad area that embraces all methods and techniques in different levels of human activities and knowledge gaoling to save energy, time, financial and natural resources. Accordingly, environmental sustainability as a major aspect of the concept has concerned the environmental issues such as: climate change, global warming, waste management, sound masking, etc. The principal goal of this paper is to investigate the role of public squares in new urban developments in the historic cities from the perspective of environmental sustainability. Therefore, the paper considers some examples of the city squares in a case study (Isfahan-Iran) to highlight some problems in adaptation with the new 21 st century-style of urban development in such cities. Hence, the investigation compares the original historic squares vs. some recently developed ones. The literature review of this paper is based on the data gathered from internet, books and journals and previously published conference papers. Moreover, a qualitative research has been conducted through local observation and survey in the location of the case study (Isfahan-Iran). The results will reveal the major principles of environmental sustainability in design of new public squares in such cities. This, in turn, opens new doors to future studies about adoption of old cities with new developments regarding to the concept of environmental sustainability.

Multiple maskers for speech masking in open-plan offices

Sound masking is an effective method to reduce speech intelligibility for reaching acceptable speech privacy in open-plan offices. Speech-like masker is considered as a good choice to reduce speech intelligibility. Using one masker in masking system is the common way so far. In this paper, a new method was proposed, using randomly integrated speech frames (SF) of the speaker as masker. Because SF masker was based on speech of the same speaker, it is a good speech-like masker. We further studied the method of using multiple SF maskers. The performance of this new masking method was evaluated by objective measurement (STOI). The speech masked by one SF masker and multiple SF maskers were compared. Results showed that speech with SF masker could reduce speech intelligibility. Speech with multiple SF maskers led to poorer speech intelligibility than speech with only one SF masker. Masking speech by multiple SF maskers is an effective way to reduce speech intelligibility in open-plan offices. (Acknowledgement: This research was supported by the joint training PhD program of Chinese Academy of Sciences-Fraunhofer, and Fraunhofer Institute of Building Physics in Stuttgart, Germany.)

The neural basis for energetic and informational masking effects in speech perception

Functional imaging studies of speech perception have revealed extensive involvement of the dorsolateral temporal lobes in aspects of speech and voice processing. In the current study, fMRI was used as a functional imaging method to address the perception of speech in different masking conditions. Throughout the scanning experiment, subjects were directed to listen to a female talker with whom they had been familiarized previously. In addition to the acoustic noise generated by the scanner, different kinds of masking sound were also presented diotically, at SPL levels determined by pilot testing. The masking sounds were signal correlated noise, spectrally rotated speech, and a second female talker. The results show a network of activation in the bilateral temporal lobes, prefrontal cortex and parietal lobes that were commonly activated across all masking conditions. Controlling for the effects of energetic masking, informational masking gave rise exclusively to clusters of activity in bilateral STG, with peak level activations in left anterior-mid STG and posterior STS/STG and right primary auditory cortex. Post-test intelligibility measures were used to reveal greater activation in the left temporal lobe, which was associated with higher performance scores.

Sound Localization in Noise by Gerbils and Humans

Detection and localization of a target sound in the presence of concurrent, spatially distributed masking sounds is one of the most challenging tasks for the mammalian auditory system. Previous studies demonstrated that the ability to localize signals is decreased by interfering noise. In order to directly compare the behavioral performance in a signal processing task in noise between gerbils and humans in the free sound field, we quantified their localization ability for a low-frequency signal in the presence of six masking noise sources surrounding the subject. Thresholds were measured both for masking noises that were correlated or uncorrelated across the masking sources. Overall, the gerbils required a higher signal/noise ratio to detect the low-frequency signal than the humans; that is, the behavioral performance of the gerbils was considerably worse than that of the humans. Moreover, switching from maskers that were uncorrelated across the masking sources to correlated maskers resulted in more masking in gerbils but in a release from masking in humans. These results would suggest that the gerbil may not be a good animal model for binaural processing. However, simulations of the localization thresholds in a numerical model of binaural processing in gerbils and humans reveal that both the inferior overall performance in gerbils and the opposite effect of masker correlation on the detection thresholds can be attributed to the smaller head size and the wider peripheral auditory filters in gerbils. Thus, the current data indicate that the binaural processor itself (i.e., the evaluation of signals coming from the two ears) is equally sensitive in gerbils and humans. However, the physical limitations imposed by the small head prevent the gerbil from performing equally well in the current paradigm.

Sound Masking Performance of Time-Reversed Masker Processed from the Target Speech

Sound Masking Performance of Time-Reversed Masker Processed from the Target Speech

Effects of Sound Masking and Screening in Offices with Conversation Noise

Effects of Sound Masking and Screening in Offices with Conversation Noise

Effect of Harmonicity on the Detection of a Signal in a Complex Masker and on Spatial Release from Masking

The amount of masking of sounds from one source (signals) by sounds from a competing source (maskers) heavily depends on the sound characteristics of the masker and the signal and on their relative spatial location. Numerous studies investigated the ability to detect a signal in a speech or a noise masker or the effect of spatial separation of signal and masker on the amount of masking, but there is a lack of studies investigating the combined effects of many cues on the masking as is typical for natural listening situations. The current study using free-field listening systematically evaluates the combined effects of harmonicity and inharmonicity cues in multi-tone maskers and cues resulting from spatial separation of target signal and masker on the detection of a pure tone in a multi-tone or a noise masker. A linear binaural processing model was implemented to predict the masked thresholds in order to estimate whether the observed thresholds can be accounted for by energetic masking in the auditory periphery or whether other effects are involved. Thresholds were determined for combinations of two target frequencies (1 and 8 kHz), two spatial configurations (masker and target either co-located or spatially separated by 90 degrees azimuth), and five different masker types (four complex multi-tone stimuli, one noise masker). A spatial separation of target and masker resulted in a release from masking for all masker types. The amount of masking significantly depended on the masker type and frequency range. The various harmonic and inharmonic relations between target and masker or between components of the masker resulted in a complex pattern of increased or decreased masked thresholds in comparison to the predicted energetic masking. The results indicate that harmonicity cues affect the detectability of a tonal target in a complex masker.

Sound Processing Hierarchy within Human Auditory Cortex

Both attention and masking sounds can alter auditory neural processes and affect auditory signal perception. In the present study, we investigated the complex effects of auditory-focused attention and the signal-to-noise ratio of sound stimuli on three different auditory evoked field components (auditory steady-state response, N1m, and sustained field) by means of magnetoencephalography. The results indicate that the auditory steady-state response originating in primary auditory cortex reflects the signal-to-noise ratio of physical sound inputs (bottom-up process) rather than the listener's attentional state (top-down process), whereas the sustained field, originating in nonprimary auditory cortex, reflects the attentional state rather than the signal-to-noise ratio. The N1m was substantially influenced by both bottom-up and top-down neural processes. The differential sensitivity of the components to bottom-up and top-down neural processes, contingent on their level in the processing pathway, suggests a stream from bottom-up driven sensory neural processing to top-down driven auditory perception within human auditory cortex.

Effects of Five Speech Masking Sounds on Performance and Acoustic Satisfaction. Implications for Open-Plan Offices

The aim of this study was to compare different sounds which can be used in open-plan offices to mask distracting speech. Fifty-four subjects were tested in seven sound conditions: speech, silence and five masked speech conditions. The five masking sounds were filtered pink noise, ventilation noise, instrumental music, vocal music and the sound of spring water. They were superimposed on speech. The masked speech conditions corresponded to an acoustically excellent open-plan office in respect to the Speech Transmission Index (STI 0.38). The speech condition (STI 0.62) corresponded to the STI obtained between nearby workstations in an acoustically poor open-plan office. Silent condition (STI 0.00) corresponded to the STI measured between two nearby private office rooms. In each of the seven sound conditions, the subjects performed a short-term memory task, a proofreading task and a creative thinking task and completed a questionnaire on acoustic comfort. Compared to silence condition, short-term memory performance deteriorated in speech condition and in most masked speech conditions. Compared to speech condition, performance improved when speech was masked with spring water sound. Ratings of acoustic satisfaction and subjective workload showed that masked speech conditions subjectively improved the working conditions compared to speech condition. Overall, the performance results and subjective perceptions showed that the spring water sound was the most optimal speech masker whereas vocal music produced negative effects similar to those of speech. The use of constant masking sounds should be preferred in open-plan offices instead of instrumental or vocal music.

실내 환경에서 쾌적성 향상을 위한 Vector Base Amplitude Panning 기반의 소음제어

A variety of noise control methods have been developed as an interest on noise issues increases. Among them, noise control methods using masking effect, a phenomenon to reduce the ability to notice the unwanted sound by proper sound, to implement a pleasant sound environment have been studied under the name of soundscape. We proposed a novel vector base amplitude panning(VBAP) based noise control method to apply to the building environment. The proposed method could improve the amenity inside the building to reproduce the sounds with excellent masking effect on the incoming path of noise using the control speakers, considering the direction of noise source. The directional masking sounds can be generated by using VBPA technique. To verify the performance of the proposed method, we carried out the subjective test for the degree of amenity according to direction of the masking sound. Subjective test results showed that it is possible to improve the amenity inside the building by controlling the direction of masking sound considering the human`s auditory characteristic.