Signal Masking Research Articles

Vibration-based bearing fault detection for operations and maintenance cost reduction in wind energy

Abstract Critical mechanical faults in wind turbine systems lead to considerable downtime and repair costs. Improving the detection and diagnosis of such faults thus brings about significant cost reductions for operations and maintenance (O&M) and electricity production. One of the most common defects in drivetrains are rolling element bearing faults. Detecting the faults in their incipient phase can prevent a more catastrophic breakdown and save a company time and money. This paper focuses on separating the bearing fault signals from masking signals coming from drivetrain elements like gears or shafts. The separation is based on the assumption that signal components of gears or shafts are deterministic and appear as clear peaks in the frequency spectrum, whereas bearing signals are stochastic due to random jitter on their fundamental period and can be classified as cyclostationary. A technique that recently gained more attention for separating these two types of signals is the cepstral editing procedure and it is investigated further in this paper as an automated procedure. The performance of the developed methods is validated on experimental data from the National Renewable Energy Laboratory (NREL) in the context of the wind turbine gearbox condition monitoring round robin study.

Nuclear Export Signal Masking Regulates HIV-1 Rev Trafficking and Viral RNA Nuclear Export.

HIV-1 infects more than 34 million people worldwide causing >1 million deaths per year. Infectious virion production is activated by the essential viral Rev protein that mediates nuclear export of intron-bearing late-stage viral mRNAs. Rev's shuttling into and out of the nucleus is regulated by the antagonistic activities of both a peptide-encoded N-terminal nuclear localization signal and C-terminal nuclear export signal (NES). How Rev and related viral proteins balance strong import and export activities in order to achieve optimal levels of viral gene expression is incompletely understood. We provide evidence that multimerization provides a mechanism by which Rev transiently masks its NES peptide, thereby biasing its trafficking to and retention within the nucleus. Targeted pharmacological disruption of Rev-Rev interactions should perturb multiple Rev activities, both Rev-RNA binding and Rev's trafficking to the nucleus in the first place.

To overlap or not to overlap: context-dependent coordinated singing in lekking long-billed hermits

When using signals to attract mates or defend resources, animals often overlap the voices of other individuals in close proximity. In such contexts signal masking is likely and animals would benefit by adopting behavioural strategies that modify the timing of signals to minimize the negative effects of masking or take advantage of its signalling value. Indeed, temporal coordination has been commonly described in a wide variety of taxa, but compelling evidence demonstrating that it arises as an active process is scarce. Here we investigate the degree of coordinated singing by lekking long-billed hermit hummingbirds, Phaethornis longirostris, in the Neotropics, using randomization tests to study the timing of vocal signals. We first demonstrate that a randomization statistical approach is robust at detecting coordinated singing in simulated data. Then, we show that long-billed hermits engage in vocal interactions in which either song alternation or song overlap is used. Furthermore, we show that singing behaviour varies with the distance between singers: hermits alternate their songs when they are in close proximity, and they overlap songs at farther distances. Birds achieve these two behaviours by modifying the time intervals between signals. The association between pattern of coordination and distance is not fully explained by any of the current hypotheses for song overlap and suggests that multiple context-dependent singing strategies could be involved. Our findings provide compelling evidence on vocal coordination as an active process in this species and validate an analytical approach that could be extended to investigate similar patterns in other taxa.

Lombard effect onset times reveal the speed of vocal plasticity in a songbird.

Animals that use vocal signals to communicate often compensate for interference and masking from background noise by raising the amplitude of their vocalisations. This response has been termed the Lombard effect. However, despite more than a century of research, little is known how quickly animals can adjust the amplitude of their vocalisations after the onset of noise. The ability to respond quickly to increases in noise levels would allow animals to avoid signal masking and ensure their calls continue to be heard, even if they are interrupted by sudden bursts of high-amplitude noise. We tested how quickly singing male canaries (Serinus canaria) exhibit the Lombard effect by exposing them to short playbacks of white noise and measuring the speed of their responses. We show that canaries exhibit the Lombard effect in as little as 300 ms after the onset of noise and are also able to increase the amplitude of their songs mid-song and mid-phrase without pausing. Our results demonstrate high vocal plasticity in this species and suggest that birds are able to adjust the amplitude of their vocalisations very rapidly to ensure they can still be heard even during sudden changes in background noise levels.

Spatial and temporal disparity in signals and maskers affects signal detection in non-human primates

Detection thresholds for auditory stimuli (signals) increase in the presence of maskers. Natural environments contain maskers/distractors that can have a wide range of spatiotemporal properties relative to the signal. While these parameters have been well explored psychophysically in humans, they have not been well explored in animal models, and their neuronal underpinnings are not well understood. As a precursor to the neuronal measurements, we report the effects of systematically varying the spatial and temporal relationship between signals and noise in macaque monkeys (Macaca mulatta and Macaca radiata). Macaques detected tones masked by noise in a Go/No-Go task in which the spatiotemporal relationships between the tone and noise were systematically varied. Masked thresholds were higher when the masker was continuous or gated on and off simultaneously with the signal, and lower when the continuous masker was turned off during the signal. A burst of noise caused higher masked thresholds if it completely temporally overlapped with the signal, whereas partial overlap resulted in lower thresholds. Noise durations needed to be at least 100 ms before significant masking could be observed. Thresholds for short duration tones were significantly higher when the onsets of signal and masker coincided compared to when the signal was presented during the steady state portion of the noise (overshoot). When signal and masker were separated in space, masked signal detection thresholds decreased relative to when the masker and signal were co-located (spatial release from masking). Masking release was larger for azimuthal separations than for elevation separations. These results in macaques are similar to those observed in humans, suggesting that the specific spatiotemporal relationship between signal and masker determine threshold in natural environments for macaques in a manner similar to humans. These results form the basis for future investigations of neuronal correlates and mechanisms of masking.

Informational masking of vocal signals in a nonhuman animal

Informational masking (IM) interferes with speech perception in the presence of multiple talkers. However, its impact on vocal communication in other animals has received little attention. This talk will present behavioral and neurophysiological evidence—much of it preliminary, circumstantial, or both—suggesting that frogs are also susceptible to IM in the context of vocal communication in noisy social environments. When choosing a mate in a chorus, female treefrogs must extract information related to a male’s suitability and quality as a mate from the temporal envelope of his vocalizations. In behavioral experiments, temporally structured maskers constrain a female’s ability to process the temporal envelopes of target vocalizations, even when targets and maskers are sufficiently different in frequency to be transduced by different inner ear papillae. (The frog’s peripheral auditory system—consisting of multiple sensory papillae that encode different frequency ranges of airborne sound—provides a natural “spectral protection zone” for minimizing the impacts of energetic masking in experimental studies of IM.) In neurophysiological experiments, potential correlates of IM can be observed in the responses of single neurons in the inferior colliculus. Future work will employ a multi-tone masking paradigm to determine how spatial separation, masker uncertainty, and target-masker similarity impact “subcortical” signal processing mechanisms in the context of IM and vocal communication.

Adaptive Gain Control for Enhanced Speech Intelligibility Under Reverberation

Overlap-masking reduces speech intelligibility in reverberant environments. In contrast to additive noise, the masking signal depends on the past of the speech signal. An increase in output signal power is followed by an increase in reverberation power. Taking into consideration, the mechanics of reverberation is essential for the development of speech modifications that effectively increase intelligibility. This letter proposes a mathematical framework that optimizes the full-band signal power as a function of late reverberation power and the degree of signal nonstationarity. The prescribed signal gain is smoothed adaptively to suppress artifacts that may be introduced by rapid gain fluctuations due to frame-based processing. Compared to a reference method, it is shown that higher signal-to-late-reverberation ratio in nonstationary regions of the speech signal is achieved with less aggressive, on average, gain modification. A listening test with native English speakers on meaningful sentences under strong reverberation measured a consistent and significant improvement in intelligibility over natural speech and a reference method.

MASKING ANTI-PHAGOCYTIC SIGNAL OF TUMOR BY PRO-PHAGOCYTIC SIGNAL-A KEY TO IMMUREMENT OF CANCER CELL

<p>Immune surveillance is a mechanism where cells and tissues are watched constantly by ever alerted immune system. Most incipient cancer cells are recognized and eliminated by the immune surveillance mechanism, but still tumors have the ability to evade immune surveillance and immunological killing. One greater arm that tumor use to evade immune surveillance, is by expressing anti-phagocytic signal (CD47). Here we present a provocative hypothesis where cancer cells are removed alive by phagocytic cell (DC). That in turn will elicit effective and higher immunogenic condition. All this could be possible by addition pro-phagocytic signal (PtdSer) over cancer cell surface (Breast Cancer), that mask the presence of anti-phagocytic signal (CD47). In other words, adding eat me signal (PtdSer) over the breast cancer cell surface that mask the presence of don’t eat me signal or anti-phagocytic signal present in breast cancer cell surface. This could be possible by using bi-specific antibody, conjugated to PEG-modified liposomes, which carry (PtdSer) pro-phagocytic signal (or) eat me signal, which target both CD47 and EGFRVIII on breast carcinoma. The simultaneous masking of anti-phagocytic signal, and adding of pro–phagocytic signal over cancer cell, will enhance the phagocytic clearance of live tumor cell and elicit immunological killing.</p>

Moderate evidence for a Lombard effect in a phylogenetically basal primate.

When exposed to enhanced background noise, humans avoid signal masking by increasing the amplitude of the voice, a phenomenon termed the Lombard effect. This auditory feedback-mediated voice control has also been found in monkeys, bats, cetaceans, fish and some frogs and birds. We studied the Lombard effect for the first time in a phylogenetically basal primate, the grey mouse lemur, Microcebus murinus. When background noise was increased, mouse lemurs were able to raise the amplitude of the voice, comparable to monkeys, but they did not show this effect consistently across context/individuals. The Lombard effect, even if representing a generic vocal communication system property of mammals, may thus be affected by more complex mechanisms. The present findings emphasize an effect of context, and individual, and the need for further standardized approaches to disentangle the multiple system properties of mammalian vocal communication, important for understanding the evolution of the unique human faculty of speech and language.

Role of Binaural Temporal Fine Structure and Envelope Cues in Cocktail-Party Listening.

While conversing in a crowded social setting, a listener is often required to follow a target speech signal amid multiple competing speech signals (the so-called "cocktail party" problem). In such situations, separation of the target speech signal in azimuth from the interfering masker signals can lead to an improvement in target intelligibility, an effect known as spatial release from masking (SRM). This study assessed the contributions of two stimulus properties that vary with separation of sound sources, binaural envelope (ENV) and temporal fine structure (TFS), to SRM in normal-hearing (NH) human listeners. Target speech was presented from the front and speech maskers were either colocated with or symmetrically separated from the target in azimuth. The target and maskers were presented either as natural speech or as "noise-vocoded" speech in which the intelligibility was conveyed only by the speech ENVs from several frequency bands; the speech TFS within each band was replaced with noise carriers. The experiments were designed to preserve the spatial cues in the speech ENVs while retaining/eliminating them from the TFS. This was achieved by using the same/different noise carriers in the two ears. A phenomenological auditory-nerve model was used to verify that the interaural correlations in TFS differed across conditions, whereas the ENVs retained a high degree of correlation, as intended. Overall, the results from this study revealed that binaural TFS cues, especially for frequency regions below 1500 Hz, are critical for achieving SRM in NH listeners. Potential implications for studying SRM in hearing-impaired listeners are discussed. Acoustic signals received by the auditory system pass first through an array of physiologically based band-pass filters. Conceptually, at the output of each filter, there are two principal forms of temporal information: slowly varying fluctuations in the envelope (ENV) and rapidly varying fluctuations in the temporal fine structure (TFS). The importance of these two types of information in everyday listening (e.g., conversing in a noisy social situation; the "cocktail-party" problem) has not been established. This study assessed the contributions of binaural ENV and TFS cues for understanding speech in multiple-talker situations. Results suggest that, whereas the ENV cues are important for speech intelligibility, binaural TFS cues are critical for perceptually segregating the different talkers and thus for solving the cocktail party problem.

Airport noise predicts song timing of European birds

Anthropogenic noise is of increasing concern to biologists and medical scientists. Its detrimental effects on human health have been well studied, with the high noise levels from air traffic being of particular concern. However, less is known about the effects of airport noise pollution on signal masking in wild animals. Here, we report a relationship between aircraft noise and two major features of the singing behavior of birds. We found that five of ten songbird species began singing significantly earlier in the morning in the vicinity of a major European airport than their conspecifics at a quieter control site. As birds at both sites started singing before the onset of air traffic in the morning, this suggests that the birds in the vicinity of the airport advanced their activity to gain more time for unimpaired singing before the massive plane noise set in. In addition, we found that during the day, chaffinches avoided singing during airplane takeoffs, but only when the noise exceeded a certain threshold, further suggesting that the massive noise caused by the airport can impair acoustic communication in birds. Overall, our study indicates that birds may be adjusting their mating signals and time budgets in response to aircraft noise.

Vibration-based bearing fault detection on experimental wind turbine gearbox data

Rolling element bearing faults are one of the most common defects in rotating machinery. The detection of these faults has lately attracted an increasing amount of attention in the industry. Detecting the faults in their incipient phase can prevent a more catastrophic breakdown of a machine and can save a company time and money. An often occurring problem in analyzing vibration measurements of a rotating machine is the presence of harmonic signal components originating from different machine parts. This paper focuses on separating the bearing fault signals from other masking signal content coming from elements like gears or rotating shafts. The separation is based on the assumption that signal components of gears or shafts are deterministic and appear as clear peaks in the frequency spectrum, whereas bearing signals are stochastic due to random jitter on their fundamental period and can be classified as cyclostationary. A technique that has recently gained more attention for separating these two types of signals is the cepstral editing procedure (CEP). This preprocessing method is investigated further in this paper as an automated procedure. The cepstral editing procedure makes use of the fact that deterministic components appear in the cepstrum as narrow peaks and removal of these cepstral peaks reduces the amplitude of the corresponding discrete components. The residual stochastic signal after cepstral editing should consist mainly out of bearing fault signals in certain frequency bands. To analyze the residual signal the squared envelope spectrum is examined. The issue of selecting the proper frequency band where to demodulate the signal necessary for enveloping is addressed through the use of spectral kurtosis. The performance of the developed methods will be validated on experimental data from the National Renewable Energy Laboratory (NREL). This data has been made available by NREL in the context of the wind turbine gearbox condition monitoring round robin study. As such other research teams from around the world have analyzed this data as well and published their findings. The measurements were done on a wind turbine gearbox in a healthy and damaged condition and the setup is documented extensively, making it well suited fora performance comparison. A summary of the findings on the NREL data is discussed in this paper.

Effects of noise generated by construction sites on wild birds

Noise generated from human activities (in particular by infrastructure and construction sites) can have a strong impact on the physiology and behavior of birds. In this work, a quantitative method for evaluating the impact of noise on wild birds is proposed. The method combines the results of previous studies that considered the effect of noise on birds and involved noise mapping evaluations. A forecast noise simulation was used to generate maps of (1) signal masking areas and (2) potential density variation. These results allow the determination of the highest risk areas for wild birds.

The Lombard effect in male ultrasonic frogs: Regulating antiphonal signal frequency and amplitude in noise.

Acoustic communication in noisy environments presents a significant challenge for vocal animals because noise can interfere with animal acoustic signals by decreasing signal-to-noise ratios and masking signals. Birds and mammals increase call intensity or frequency as noise levels increase, but it is unclear to what extend this behavior is shared by frogs. Concave-eared torrent frogs (Odorrana tormota) have evolved the capacity to produce various calls containing ultrasonic harmonics and to communicate beside noisy streams. However, it is largely unclear how frogs regulate vocalization in response to increasing noise levels. We exposed male frogs to various levels of noise with playback of conspecific female courtship calls and recorded antiphonal signals and spontaneous short calls. Males were capable of rapidly adjusting fundamental frequency and amplitude of antiphonal signals as noise levels increased. The increment in fundamental frequency and amplitude was approximately 0.5 kHz and 3 dB with every 10 dB increase in noise level, indicating the presence of noise-dependent signal characteristics. Males showed the noise-tolerant adaption in response to female calls in noise level from 40 to 90 dB SPL. The results suggest that the noise-dependent signal characteristics in O. tormota have evolved as a strategy to cope with varying torrent noise.

Blind image counterwatermarking \u2013 hidden data filter

Watermarking is a dynamically developing method of copyright protection used for media (sounds, images, films, or 3D objects) that employs signal processing in order to hide additional, invisible information about the owner or author. However, studies until now have not widely considered the problem of attempting to blind removal of hidden data in a manner that allows the watermarked signal to be returned to the original signal. Current considerations of authors of leading articles in the watemarking field focus on the robustness of the method – security system against intentional attacks of removal of the additional information, without taking into account the aspect of simultaneous degradation of the quality and form of the watermarked picture. As has been shown in the article, it is possible to design a perfect filter (same as reversible operations) that allows the removal of additional information from the watermarked picture in a way that makes it possible to return to the form of the host image. This paper describes an ideal filter used for removal of additional, invisible information in forms of an eliminating function and a signal masking function. Their effectiveness has been demonstrated for practical implementations of this type of eliminating and masking filters for watermarking methods in the cepstrum domain.

Low frequency dove coos vary across noise gradients in an urbanized environment

Urbanization poses a challenge to bird communication due to signal masking by ambient noise and reflective surfaces that lead to signal degradation. Bird species (especially oscines) have been shown to alter their singing behaviour to increase signal efficiency in highly urbanized environments. However, few studies on the effects of noise on song structure have included birds with low frequency vocal signals which may be especially vulnerable to noise pollution due to significant frequency overlap of their signals with traffic noise. We compared the perch coos of spotted doves (Streptopelia chinensis), a species with very low frequency vocalizations, in different background noise levels across urban and peri-urban areas in Hong Kong. We documented a 10% upward shift in the minimum frequency of coos of spotted doves across the noise gradient (a relatively small but significant shift), and a reduced maximum frequency in urban habitats with a higher density of built up area. Hong Kong doves had significantly higher minimum and maximum frequencies than doves from throughout their range (from mostly rural sites). Our results indicate that urban species with extremely low sound frequencies such as doves can alter their vocalizations in response to variable urban acoustic environments.

Fault Diagnosis of On-Load Tap-Changer in Converter Transformer Based on Time–Frequency Vibration Analysis

The suitable condition of an on-load tap-changer (OLTC) is essential for the operation of converter transformer due to its frequent switch for the voltage regulation of power system. This paper describes a methodology to obtain the OLTC vibration characteristics in time–frequency domain. Considering the possible aliasing effect in vibration signal processing, an improved empirical mode decomposition (EMD) is proposed with masking signals of multiple frequencies added, which has obvious superiority in aliasing reduction compared with conventional methods. Then, an effective fault-diagnosis strategy based on energy distributions variations of OLTC vibration signals according to Lorentz information measure is brought up. The calculated results under normal and typical fault conditions of model and real OLTC have shown that the energy spectrums of different conditions vary significantly so that the similarity index can measure the difference degree of energy distribution. Meanwhile, the index of contact looseness is higher than the insulated panel looseness which indicates that the contact looseness fault has greater influence on switch-over process of OLTC.

Gauging allowable harm limits to cumulative, sub-lethal effects of human activities on wildlife: A case-study approach using two whale populations

As sublethal human pressures on marine wildlife and their habitats increase and interact in complex ways, there is a pressing need for methods to quantify cumulative impacts of these stressors on populations, and policy decisions about allowable harm limits. Few studies quantify population consequences of individual stressors, and fewer quantify synergistic effects. Incorporating all sources of uncertainty can cause predictions to span the range from negligible to catastrophic. Two places were identified to bound this problem through energetic mechanisms that reduce prey available to individuals. First, the US Marine Mammal Protection Act's Potential Biological Removal (PBR) equation was used as a placeholder allowable harm limit to represent the number of animals that can be removed annually without depleting a population below agreed-upon management targets. That rephrased the research question from, “How big could cumulative impacts be?” to “How big would cumulative impacts have to be to exceed an agreed-upon threshold?” Secondly, two data-rich case studies, namely Gulf of Maine humpback and northeast Pacific resident killer whales, were used as examples to parameterize the weakest link, namely between prey availability and demography. Given no additional information, the model predicted that human activities need only reduce prey available to the killer whale population by ~10% to cause a population-level take, through reduced fecundity and/or survival, equivalent to PBR. By contrast, in the humpback population, reduction in prey availability of ~50% was needed to cause a similar, PBR-sized effect. The paper describes an approach – results are merely illustrative. The two case studies differ in prey specialization, life history, and, no doubt, proximity to carrying capacity. This method of inverting the problem refocuses discussions around what the level of prey depletion – via competition with commercial fisheries, displacement from feeding areas through noise-generating activities, or acoustic masking of signals used to detect prey – would have to occur to exceed allowable harm limits set for lethal takes in fisheries or other, more easily quantifiable, human activities.

Behavioural responses to sound exposure in captivity by two fish species with different hearing ability

Underwater sound generated by human activities is increasing in, on and near aquatic environments. Such anthropogenic noise can induce artificially elevated ambient sound levels and cause various detrimental effects in fish, such as temporary or permanent hearing loss, masking of relevant acoustic signals and cues or behavioural changes that may have fitness consequences. Also, captive fish are often exposed to noisy conditions, which may have consequences for production in aquaculture, biases in scientific results in laboratories or welfare in hobby aquaria. However, we still have limited insight into how fish cope with artificial sound exposure and how species differ in sensitivity. Here, we compared zebrafish, Danio rerio, and Lake Victoria cichlids, Haplochromis piceatus, the former being sensitive to lower absolute thresholds and wider spectral ranges than the latter. Experimental sound exposure induced a significant reduction in swimming speed in the first minute of exposure for both species in captive conditions. Furthermore, zebrafish showed clear startle response behaviour with the onset of the sound exposure leading to an initial, brief increase in swimming speed, which was not found for the cichlids. Neither species showed spatial shifts away from the active speaker in the horizontal plane, but cichlids shifted downwards to spend more time in the bottom area of the fish tank after the onset of sound exposure, while zebrafish retained their average swimming height during the same exposure levels. Our results show that sound exposure can cause both similar and species-specific responses in two fish species and that these responses are not obviously related to differences in their hearing ability.

Comparison of Blackman, linear rise-fall, and linear rise-fall chirp signals in backward masking

Backward masking is finding applications in clinical testing and the diagnosis of auditory processing disorders. Masking of a tonal signal by a band-limited noise in a backward masking paradigm requires significant vigilance and produces fatigue. This study compared the backward masking functions of ten normal hearing young (18–30 years) subjects using tonal stimuli with different signatures in order to provide a better contrast to the noise masker. Subjects adaptively tracked the tonal threshold using 2 dB changes. The noise stimulus was 70 dB HL, and the inter-stimulus interval (ISI) varied from 2 ms to 64 ms. The results will be described in terms of fatigue, tracking efficiency, and latency.