High Levels Of Background Noise Research Articles

Bypassing the Bottleneck: The Advantage of Fingertip Shear Feedback for Navigational Cues

Multiple resource models suggest that there will be less interference between tasks that do not share the same processing resources or modalities. Most in-vehicle navigational systems rely on some type of auditory modality, which can be problematic in situations with high levels of background noise or when one is engaged in a secondary auditory task, such as talking on a cell phone. The haptic or tactile sensory modality may be an effective alternative for presenting important navigational information in a vehicle. The current study compared the effectiveness of auditory vs. tactile navigational instructions to the operator of a moving vehicle. Tactile shear cues were provided to the participants' index fingers as they gripped the steering wheel. These tactile cues provided directional information that coincide with the direction of the applied skin displacement. In single task driving, participants made accurate lane changes in response to both auditory and tactile instructions. In dual-task driving, where participants conversed on a cell phone, participants were less accurate with auditory instructions than for tactile instructions. This suggests that in some instances, presenting information via the tactile modality may bypass the bottleneck described by multiple resource theories when there is competition for the same resources.

Reliable detection of predator cues in afferent spike trains of a katydid under high background noise levels

Katydid receivers face the problem of detecting behaviourally relevant predatory cues from echolocating bats in the same frequency domain as their own conspecific mating signals. We therefore tested the hypothesis that katydids are able to detect the presence of insectivorous bats in spike discharges at early stages of nervous processing in the auditory pathway by using the temporal details characteristic for responses to echolocation sequences. Spike activity was recorded from an identified nerve cell (omega neuron) under both laboratory and field conditions. In the laboratory, the preparation was stimulated with sequences of bat calls at different repetition rates typical for the guild of insectivorous bats, in the presence of background noise. The omega cell fired brief high-frequency bursts of action potentials in response to each bat sound pulse. Repetition rates of 18 and 24 Hz of these pulses resulted in a suppression of activity resulting from background noise, thus facilitating the detection of bat calls. The spike activity typical for responses to bat echolocation contrasts to responses to background noise, producing different distributions of inter-spike intervals. This allowed development of a 'neuronal bat detector' algorithm, optimized to detect responses to bats in afferent spike trains. The algorithm was applied to more than 24 hours of outdoor omega-recordings performed either at a rainforest clearing with high bat activity or in rainforest understory, where bat activity was low. In 95% of cases, the algorithm detected a bat reliably, even under high background noise, and correctly rejected responses when an electronic bat detector showed no response.

Evaluation of P300-Based Brain-Computer Interface in Real-World Contexts

Despite recent advances in brain-computer interface (BCI) development, system usability still remains a large oversight. The goal of this study was to investigate the usability of a P300-based BCI system, P300 Speller, by assessing how background noise and interface color contrast affect user performance and BCI usage preference. Fifteen able-bodied participants underwent a 2 (low and high interface color contrast) × 3 (low, medium, and high background noise level) within-subjects design experiment, in which participants were asked to type six 10-character phrases in the P300 Speller paradigm. The overall accuracy in the study was 80.2%. Participants showed higher accuracy, higher information transfer rate, bigger amplitude, and smaller latency in the high interface color contrast condition than in the low contrast condition. Participants had better performance in the noisy condition than in the quiet condition, but the background noise effects were not statistically significant in the present study. These results should give some insight to the real-world applicability of the current P300 Speller as a nonmuscular communication system, especially for individuals with severe neuromuscular disabilities.

Urban acoustic and seismic noise measurements in Baltimore.

Acoustic and seismic sensors have good potential for passive, non‐line‐of‐sight, detection, localization, and monitoring of natural and human activities. However, to fulfill this potential, sensor algorithms must be designed to not only robustly identify signals of interest but also to cope with environmental effects including high levels of background noise often found in urban areas. This paper presents experimental measurements conducted in Baltimore and at other locations to investigate noise levels in rural, urban, and industrial environments for audio frequencies between 6 Hz and 20 kHz and seismic frequencies from 6 to 1000 Hz. Because of the interest in large‐scale Earth studies, there are hardly any previous seismic measurements in this high‐frequency band and also most were done in remote areas specifically to avoid cultural noise. The measured urban seismic spectra tend to have more structure and variation in shape from one location to another compared to the acoustic spectra, and a more rapid decay with increasing frequency, usually about 30 dB from 30 to 600 Hz. The urban acoustic peak frequency is usually around 60 Hz, while the peak seismic frequencies are usually less than 25 Hz. [Work funded by U.S. Army.]

Whispering arches as intimate soundscapes.

Whispering archways are whispering galleries. They are sometimes found around smooth arches, doorways, and even bridges. Persons positioned on opposite sides of a whispering arch communicate privately by whispering into the arch. In that way they function as private and even intimate soundscapes. Some whispering arches that have stood for centuries have inspired local folk legends. Such acoustical architecture can help to establish a sense of place and strengthen emotional ties. It is said that a whispering arch at the entrance to a 10th c. Gothic cathedral at the historic monastic site of Clonmacnoise in the Irish midlands figured in local courtship for centuries. There, shy young lovers are said to have uttered vows of love and proposals of marriage. The arch was also used by lepers to give confession without infecting the priest. Whispering arches were almost certainly unintended in the past but can also be created intentionally as an intimate form of public art. Recent measurements on a whispering archway at West Chester University show that high background noise levels from traffic or air handlers can ruin an otherwise intimate space; however, so modern architects should plan the entire soundscape carefully.

Assessment of Teachers' Exposure to Noise in Selected Primary Schools

The assessment of teachers' exposure to noise in primary schools was carried out on the basis of: questionnaire studies (covering 187 teachers in 3 schools), noise measurements at the teachers' workplaces, measurements of the school rooms acoustic properties (reverberation time and speech transmission index STI in 72 classrooms), analysis of statistical data regarding hazards and occupational diseases in the education sector. The studies have shown that noise is the main factor of annoyance in the school environment. Over 50% of questioned teachers consider noise as annoying and near 40% as very annoying or unbearable. A-weighted equivalent continuous sound pressure levels measured in classrooms, teacher rooms and common rooms are in the range of 58-80 dB and they exceed 55 dB (criteria of noise annoyance). The most frequently reported subjective feelings and complaints (over 90%) are: growth of psychical and emotional tension, irritation, difficulties in concentrating, hoarseness, cough. Noise in schools is also a harmful factor. High A-weighted equivalent continuous sound pressure levels ranging from 80 to 85 dB, measured in corridors during pauses and in sports halls, can cause the risk of hearing damage among PE teachers and persons oversensitive to noise. The latter concerns both teachers and pupils. High background noise levels (55-65 dB) force teachers to raise their voice. It can lead to the development of an occupational disease - chronic voice disorders due to excessive vocal effort lasting for at least 15 years. In the education sector 785 new cases of this disease were reported only in 2008. Poor acoustics in classrooms (reverberation time ranging from 0.8 to 1.7 s, STI<0.6 in 50% of classrooms) have an adverse influence on speech reception and make the teaching and learning processes difficult.

Auditory evoked potentials for monitoring during anaesthesia: A study of data quality

The auditory evoked potential termed the middle latency response (MLR) has been suggested as an indicator of adequacy of anaesthesia during surgery. However, the response is small and must be extracted from high levels of background noise. A key consideration in using the MLR for clinical monitoring is whether data quality is sufficient to detect small changes. The aim of this study was to investigate the quality of the MLR recorded during anaesthesia, as a rigorous analysis of data quality is lacking in many studies. MLR recordings from patients sedated in intensive care after cardiac surgery were compared to recordings from a reference group of young volunteers with normal hearing. Data quality was measured with the F sp parameter. A bootstrap analysis was used to measure statistical response presence and to detect within-subject changes during clinical anaesthesia. Noise levels were high in the normative group probably due to myogenic and EEG activity. With 5 Hz click stimulation, MLR presence in the normative group was below 30%. Response presence improved using stimulation paradigms with chirps or maximum length sequences and reached 100% with a combination of maximum length sequences and chirps. F sp values generally improved during anaesthesia as noise levels reduced and MLR presence was 100% for MLS click stimulation. Changes in the MLR amplitude with propofol infusion rate were small. Some within-subject changes in MLR amplitude were detected using the bootstrap analysis, but 100% detection was not possible. Conclusion: Obtaining good quality MLR data in awake subjects is challenging. Data quality improves during clinical anaesthesia and with advanced stimulation methods, but reliable detection of changes in the MLR for clinical monitoring remains a challenge.

Behavioral measures of signal recognition thresholds in frogs in the presence and absence of chorus-shaped noise

Anuran amphibians are superb animal models for investigating the mechanisms underlying acoustic signal perception amid high levels of background noise generated by large social aggregations of vocalizing individuals. Yet there are not well-established methods for quantifying a number of key measures of auditory perception in frogs, in part, because frogs are notoriously difficult subjects for traditional psychoacoustic experiments based on classical or operant conditioning. A common experimental approach for studying frog hearing and acoustic communication involves behavioral phonotaxis experiments, in which patterns of movement directed toward sound sources indicate the subjects' perceptual experiences. In this study, three different phonotaxis experiments were conducted using the same target signals and noise maskers to compare different experimental methods and analytical tools for deriving estimates of signal recognition thresholds in the presence or absence of "chorus-shaped noise" (i.e., artificial noise with a spectrum similar to that of real breeding choruses). Estimates of recognition thresholds based on measures of angular orientation, response probabilities, and response latencies were quite similar in both two-choice and no-choice phonotaxis tests. These results establish important baselines for comparing different methods of estimating signal recognition thresholds in frogs tested in various masking noise conditions.

Comprehension of Speeded Discourse by Younger and Older Listeners

Researchers have argued that older adults are more adversely affected by speeding speech than are younger adults. However, the age effects usually occur when (1) the speech materials are artificially speeded to rates well above those that occur in natural speech; (2) the speeding method introduces distortions that tax the older adult's auditory processes; and (3) the speech materials are simple sentences or very short passages. This study evaluated whether older adults are disadvantaged when listening to extended discourse (10- to 15-min lectures) speeded to a rate near to the limit of normally encountered fast speech (240 words/min) with a minimum of acoustic distortion. Perceptual difficulty was further manipulated by presenting stimuli in either quiet or with a 12-talker background babble. Younger and older adults had more difficulty recalling the details of the discourse and integrating their contexts when stimuli were presented at faster rates and in higher levels of background noise. Although each of these manipulations were found to cause large differences in performance, the age groups were generally found to perform analogously in most conditions. Potentially the availability of semantically rich materials, and the extended durations of the passages, allowed the older adults an opportunity to adjust to the faster speech rates and maintain performance levels similar to younger adults.

Compact microphone array processing for in-vehicle voice detection applications.

The main goal of voice activity detection algorithms is to determine the presence of human voice signals in a given environment. Voice activity detection is very challenging in vehicle interiors. The main challenge in detecting the presence of voice signals in vehicles is the presence of a large number of interferers and a high background noise level. Further, many types of interferers such as tire or engine noise have signals that are highly nonstationary. In this work, compact microphone arrays mounted in various locations within a vehicle are used to extract signals from locations of interest. Experimental comparisons of the performance of several voice activity detection algorithms are made for various array configurations (including single microphone) and source extraction processing algorithms. Processing algorithms considered include blind source separation algorithms such as fastICA, transfer function based inversion methods, and both fixed and adaptive beamforming techniques. The performance of compact arrays is also compared to the performance of larger distributed microphone arrays. It is shown that the use of compact microphone arrays can significantly improve voice activity detection algorithms. The gain is quantified using receiver operating characteristic type curves plotting probability of detection vs probability of false alarm.

Simulation results of a veto counter for the ClearPEM

The Crystal Clear Collaboration (CCC) has built a prototype of a novel positron emission tomograph dedicated to functional breast imaging, the ClearPEM. The ClearPEM uses the common radio pharmaceutical FDG for imaging cancer. As FDG is a rather non-specific radio tracer, it accumulates not only in cancer cells but in all cells with a high energy consumption, such as the heart and liver. This fact poses a problem especially in breast imaging, where the vicinity of the heart and other organs to the breast leads to a high background noise level in the scanner. In this work, a veto counter to reduce the background is described. Different configurations and their effectiveness were studied using the GATE simulation package.

A comparison of phonological errors made by native and non-native listeners.

Previous studies have shown that listeners have difficulty recognizing non‐native words in noise [Mayo et al. (1997)] and affective prosody in quiet [Dromey et al. (2005)]. Difficulty increases with less L2 ability. Findings from the current study support these results while indicating that non‐native listeners have additional difficulty identifying prosodic patterns (i.e., those indicating sentence type) and using semantic information under high levels of background noise. Participants heard sentences presented in −2, −4, −6, and −8‐dB S/N. Target words were semantically predictable or unpredictable. Participant identification of sentence type and target words was recorded and analyzed. Both groups were affected by increasing levels of noise, but non‐natives more strongly. Semantics aided native speakers under high levels of noise, but non‐native speakers under low levels of noise. Analysis of phonological errors shows that the most frequent phonological error was on the onset and vowel, but this was not...

A hybrid MLS technique for room impulse response estimation

The measurement of room impulse response (RIR) when there are high background noise levels frequently means one must deal with very low signal-to-noise ratios (SNR). If such is the case, the measurement might yield unreliable results, even when synchronous averaging techniques are used. Furthermore, if there are non-linearities in the apparatus or system time variances, the final SNR can be severely degraded. The test signals used in RIR measurement are often disturbed by non-stationary ambient noise components. A novel approach based on the energy analysis of ambient noise – both in the time and in frequency – was considered. A modified maximum length sequence (MLS) measurement technique, referred to herein as the hybrid MLS technique, was developed for use in room acoustics. The technique consists of reducing the noise energy of the captured sequences before applying the averaging technique in order to improve the overall SNRs and frequency response accuracy. Experiments were conducted under real conditions with different types of underlying ambient noises. Results are shown and discussed. Advantages and disadvantages of the hybrid MLS technique over standard MLS technique are evaluated and discussed. Our findings show that the new technique leads to a significant increase in the overall SNR.

A Principal Component Analysis of Acoustic Emission Signals from a Landing Gear Component

This work forms part of a larger investigation into fracture detection using acoustic emission (AE) during landing gear airworthiness testing. It focuses on the use of principal component analysis (PCA) to differentiate between fracture signals and high levels of background noise. An artificial acoustic emission (AE) fracture source was developed and additionally five sources were used to generate differing AE signals. Signals were recorded from all six artificial sources in a real landing gear component subject to no load. Further to this, artificial fracture signals were recorded in the same component under airworthiness test load conditions. Principal component analysis (PCA) was used to automatically differentiate between AE signals from different source types. Furthermore, successful separation of artificial fracture signals from a very high level of background noise was achieved. The presence of a load was observed to affect the ultrasonic propagation of AE signals.

Statistical Analyses of Temporal Information in Auditory Brainstem Responses to Tones in Noise: Correlation Index and Spike-distance Metric

Gai and Carney (J Neurophysiol 96:2451-2464, 2006) previously explored the detection of tones in noise based on responses in the anteroventral cochlear nucleus; that study focused on temporal information in discharge reliability and analyses of neural responses related to the fine structure or envelope of the stimulus. Two additional temporal approaches, the correlation index (Joris et al., Hearing Res 216-217:19-30, 2006) and the spike-distance metric (Victor and Purpura, J Neurophysiol 76:1310-1326, 1996; Netw Comput Neural Syst 8:127-164, 1997), are tested in the present study. Trends in the correlation index as a function of stimulus level are similar to those of the synchronization coefficient (also called the vector strength) when the tone is presented alone. However, the present study found that trends in the correlation index did not agree with those of the synchronization coefficient for tones presented with relatively high-level background noise. Instead, trends in the correlation index generally agreed with those of the temporal reliability metric discussed in Gai and Carney (J Neurophysiol 96:2451-2464, 2006); that is, the correlation index decreased with increased tone level in the presence of relatively high-level background noise. The spike-distance metric, which was based on absolute spike times or on interspike intervals, was compared to the temporal measures described above, which were generally based on relative spike times. The results confirm that the spike-distance metric is not an optimal temporal metric. In addition, absolute spike times of primary-like responses generally contained much less temporal information than absolute spike times of chopper response types. The present study highlights the importance of relative spike-timing information as characterized by traditional and novel temporal measures.

Detection of &lt;I&gt;Anoplophora glabripennis&lt;/I&gt; (Coleoptera: Cerambycidae) Larvae in Different Host Trees and Tissues by Automated Analyses of Sound-Impulse Frequency and Temporal Patterns

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), an invasive pest quarantined in the United States, is difficult to detect because the larvae feed unseen inside trees. Acoustic technology has potential for reducing costs and hazards of tree inspection, but development of practical methods for acoustic detection requires the solution of technical problems involving transmission of resonant frequencies in wood and high background noise levels in the urban environments where most infestations have occurred. A study was conducted to characterize sounds from larvae of different ages in cambium, sapwood, and heartwood of bolts from three host tree species. Larval sounds in all of the tested trees and tissues consisted primarily of trains of brief, 3-10-ms impulses. There were no major differences in the spectral or temporal pattern characteristics of signals produced by larvae of different ages in each tissue, but larval sounds in sapwood often had fewer spectral peaks than sounds in cambium and heartwood. A large fraction, but not all background sounds could be discriminated from larval sounds by automated spectral analyses. In 3-min recordings from infested bolts, trains containing impulses in patterns called bursts occurred frequently, featuring 7-49 impulses separated by small intervals. Bursts were rarely detected in uninfested bolts. The occurrence of bursts was found to predict infestations more accurately than previously used automated spectral analyses alone. Bursts and other features of sounds that are identifiable by automated techniques may ultimately lead to improved pest detection applications and new insight into pest behavior.

Detection of Anoplophora glabripennis (Coleoptera: Cerambycidae) Larvae in Different Host Trees and Tissues by Automated Analyses of Sound-Impulse Frequency and Temporal Patterns

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), an invasive pest quarantined in the United States, is difficult to detect because the larvae feed unseen inside trees. Acoustic technology has potential for reducing costs and hazards of tree inspection, but development of practical methods for acoustic detection requires the solution of technical problems involving transmission of resonant frequencies in wood and high background noise levels in the urban environments where most infestations have occurred. A study was conducted to characterize sounds from larvae of different ages in cambium, sapwood, and heartwood of bolts from three host tree species. Larval sounds in all of the tested trees and tissues consisted primarily of trains of brief, 3–10-ms impulses. There were no major differences in the spectral or temporal pattern characteristics of signals produced by larvae of different ages in each tissue, but larval sounds in sapwood often had fewer spectral peaks than sounds in cambium and heartwood. A large fraction, but not all background sounds could be discriminated from larval sounds by automated spectral analyses. In 3-min recordings from infested bolts, trains containing impulses in patterns called bursts occurred frequently, featuring 7–49 impulses separated by small intervals. Bursts were rarely detected in uninfested bolts. The occurrence of bursts was found to predict infestations more accurately than previously used automated spectral analyses alone. Bursts and other features of sounds that are identifiable by automated techniques may ultimately lead to improved pest detection applications and new insight into pest behavior.

A Linear Programming Approach to Cross-Layer Optimization in Multiclass VSG-CDMA Over Rayleigh Fading

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a new linear programming approach for throughput maximization on the uplink of a multiclass variable spreading gain code-division multiple-access (CDMA) multicellular system in Rayleigh fading for both binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) modulations. Based on the improved Gaussian approximation technique, we derive exact closed-form expressions of the outage probability, which are used as a physical (PHY) layer constraint of the maximization problem. We show that it is possible to transform the nonlinear constraint into a set of equivalent linear expressions. This facilitates the formulation of a new linear throughput maximization that noticeably requires less computational complexity than the known nonlinear approaches. Furthermore, due to the simplicity of the linear approach, we can include the constraints of such higher layers, i.e., media access control (MAC) and call admission control (CAC) layers, into the proposed formula. Accordingly, we introduce two linear programming optimization formulas. One is for MAC-PHY optimization, and another is for cross-layer optimal CAC policy. In the case of MAC-PHY optimization, the throughput is maximized, at low background noise level, when every user retains the same bit energy, particularly in the case where the difference in data rates is high. Nonetheless, at high levels of background noise, the throughput would be maximized when a larger amount of bit energy is allocated to the high-rate users. For the joint optimal policy, the throughput and the blocking probability are optimized and improved up to 50% in comparison to those of the conventional CAC policy, which is known as the <emphasis emphasistype="boldital">complete sharing</emphasis> policy. </para>

Results of acoustical treatments in existing classrooms

In 2001, 2002, and 2005, the Department of Energetics of the Politecnico di Torino has carried out in‐field objective and subjective surveys with the aim of evaluating the acoustical quality in secondary‐school classrooms of the Province of Turin (Italy). From the results the following main problems emerged: high reverberation times, high background noise levels caused mainly by low sound insulation between classrooms and corridors and between adjacent classrooms, low façade sound insulation, excessive teachers' vocal efforts. In this work results of acoustical treatments in some of these existing classrooms are reported. Measurements are made before and after the restorations. The case studies are chosen with reference to different building typologies and urban contexts, and consisted of improvements in sound absorption, sound insulation of internal partitions, doors and façades, and acoustic bridges elimination. They are divided in “light” and “heavy” types. The first, less expensive, with the aim to obtain good acoustical conditions, the latter, more expansive, focused to obtain optimal conditions. In fact, mainly in restoration of public schools, a good level of acoustical quality with contained costs is requested. The treatments are carried out with the aim to constitute a repertory of solutions to apply primarily in school restoration.

Measuring Sound Insulation using Deconvolution Techniques

To compare the acoustic performance of a building element with the given sound insulation requirements, measurements need to be done. Generally, a broadband noise source is used according to international standards. This method does not always work in practice due to high sound insulation values or high background noise levels. It is very inconvenient from a practical point of view or even impossible to perform an accurate sound insulation measurement for all frequency bands. A solution to this problem can be found in deconvolution techniques using mls or sweep signals. It is possible to increase the signal to noise ratio with these techniques by averaging measurements and spreading out the spectral sound energy in time. As a result an efficient use of available sound power is possible. In a laboratory is investigated how to use mls or sweep signals as a source signal and deconvolution as a measurement technique to obtain the sound insulation under noisy conditions.