High Levels Of Background Noise Research Articles

Robust word boundary detection using fuzzy logic

A pattern recognition approach to robust word boundary detection in adverse acoustic noise conditions is proposed. The algorithm uses four simple differential parameters calculated in the time domain and pattern matching based on a set of six fuzzy rules extracted by a hybrid learning tool. The experimental results demonstrate that the new endpoint detector outperforms traditional methods, in particular in the presence of high levels of background noise.

A video-based performance in noise test for measuring audio-visual disability in young school children: test development, with validation by trained teachers, parents and audiometry as relative standards for disability

Background: impaired ability to detect target sounds in noisy surroundings is a particular feature of children with a history of otitis media with effusion (OME). Children with current OME are also likely to experience difficulty in speech reception in classrooms where a high level of background noise has been recorded. No tests are currently available which are feasible in primary care and which objectively measure school-related disabilities. The effects of speech in noise and the extent to which this is offset by speech reading contribute important dimensions to disability. Methods: a video-based speech reception test has been developed using the same principles in 227 English and 182 Danish 4–8 year-old children. Distribution data was collected for both language versions of the test. The test has been compared with audiometry and teacher and parents assessments to establish its validity. Interpretation: there are no gold standards for audio-visual disability in current clinical use. The poor positive predictive value of audiometry for likely classroom functioning is a cause for concern, particularly in relation to inappropriate referral of children by primary care physicians.

THE ENHANCEMENT OF IMPULSIVE NOISE AND VIBRATION SIGNALS FOR FAULT DETECTION IN ROTATING AND RECIPROCATING MACHINERY

Impulsive sound and vibration signals in machinery are often caused by the impacting of components and are commonly associated with faults. It has long been recognized that these signals can be gainfully used for fault detection. However, it tends to be difficult to make objective measurements of impulsive signals because of the high levels of background noise. This paper presents an enhancement scheme to aid the measurement and characterization of such impulsive sounds, called a two-stage Adaptive Line Enhancer (ALE), which exploits two adaptive filter structures in series. The resulting enhancer signals are analyzed in the time–frequency domain to obtain simultaneous spectral and temporal information. In order to apply the two-stage ALE successfully, the filter parameters and adaptive algorithms should be chosen carefully. Conditions for the choice of these parameters are presented and suggestions are made for suitable adaptive algorithms. Finally, the techniques developed are applied to the diagnosis of faults within an internal combustion engine and to data from an industrial gearbox.

Robust speech recognition using the modulation spectrogram

The performance of present-day automatic speech recognition (ASR) systems is seriously compromised by levels of acoustic interference (such as additive noise and room reverberation) representative of real-world speaking conditions. Studies on the perception of speech by human listeners suggest that recognizer robustness might be improved by focusing on temporal structure in the speech signal that appears as low-frequency (below 16 Hz) amplitude modulations in subband channels following critical-band frequency analysis. A speech representation that emphasizes this temporal structure, the “modulation spectrogram”, has been developed. Visual displays of speech produced with the modulation spectrogram are relatively stable in the presence of high levels of background noise and reverberation. Using the modulation spectrogram as a front end for ASR provides a significant improvement in performance on highly reverberant speech. When the modulation spectrogram is used in combination with log-RASTA-PLP (log RelAtive SpecTrAl Perceptual Linear Predictive analysis) performance over a range of noisy and reverberant conditions is significantly improved, suggesting that the use of multiple representations is another promising method for improving the robustness of ASR systems.

Assessing speech intelligibility in classrooms at the University of Washington

The University’s Committee on Accessibility has initiated an investigation of classroom acoustical conditions. This investigation has been undertaken in response to complaints made by University faculty members who state that they are experiencing difficulties in understanding student’s speech during class sessions, when students ask questions or engage in discussion. A survey of University faculty identified 75 problematic classrooms (out of the 300+ classrooms on the University campus). A sample of generally representative classrooms has been selected: these classrooms (and class sessions held in the classrooms) are being systematically measured to determine their acoustical properties. Seven parameters have been anticipated as the causes of inferior speech intelligibility: to strong background noise levels, too weak signal-to-noise ratios, excessive reverberation, too great speak-to-listener distances, various speaker idiosyncrasies (e.g., accenting, mumbling, rapidity, using unfamiliar verbiage, and so forth), acoustical defects of the classroom, and faulty amplification systems. To date, measurements show that the principal acoustical faults causing these intelligibility difficulties are high background noise levels, inadequate amounts and locations of absorptive materials and assemblies, and student speech characteristics including too-long distances separating faculty and students. In selected classrooms corrections are being undertaken.

Broadband spectra of seismic survey air-gun emissions, with reference to dolphin auditory thresholds.

Acoustic emissions from a 2120 cubic in air-gun array were recorded through a towed hydrophone assembly during an oil industry 2-D seismic survey off the West Wales Coast of the British Isles. Recorded seismic pulses were sampled, calibrated, and analyzed post-survey to investigate power levels of the pulses in the band 200 Hz-22 kHz at 750-m, 1-km, 2.2-km, and 8-km range from source. At 750-m range from source, seismic pulse power at the 200-Hz end of the spectrum was 140 dB re: 1 microPa2/Hz, and at the 20-kHz end of the spectrum seismic pulse power was 90 dB re: 1 microPa2/Hz. Although the background noise levels of the seismic recordings were far in excess of ambient, due to the proximity of engine, propeller, and flow sources of the ship towing the hydrophone, seismic power dominated the entire recorded bandwidth of 200 Hz-22 kHz at ranges of up to 2 km from the air-gun source. Even at 8-km range seismic power was still clearly in excess of the high background noise levels up to 8 kHz. Acoustic observations of common dolphins during preceding seismic surveys suggest that these animals avoided the immediate vicinity of the air-gun array while firing was in progress, i.e., localized disturbance occurred during seismic surveying. Although a general pattern of localized disturbance is suggested, one specific observation revealed that common dolphins were able to tolerate the seismic pulses at 1-km range from the air-gun array. Given the high broadband seismic pulse power levels across the entire recorded bandwidth, and known auditory thresholds for several dolphin species, we consider such seismic emissions to be clearly audible to dolphins across a bandwidth of tens on kilohertz, and at least out to 8-km range.

Comparative study of superconducting gravimeters and broadband seismometers STS-1 / Z in seismic and subseismic frequency bands

Superconducting gravimeters and broadband seismometers (vertical component) both measure gravity, but whereas the former are most sensitive to very long period signals (gravity tides with periods longer than 6 h), the latter are designed for recording the seismic band (elastic normal modes with periods shorter than 1 h). We investigate here the behaviour of each type of instrument in the spectral band where it is not generally used. More precisely, we compare the French superconducting gravimeter, located at Station J9 near Strasbourg, and the vertical component of an STS-1 seismometer located in a mine at Echery (ECH) in the Vosges, about 70 km away. Two different frequency bands are considered: the seismic band (frequencies between 0.2 and 1.667 mHz), for the study of normal modes after the Bolivian earthquake of 9 June 1994, and the subseismic band (frequencies lower than 0.2 mHz), including the study of gravity tides. The analysis of Fourier amplitude spectra and power spectral densities shows the obvious result that the broadband seismometer is more sensitive than the superconducting gravimeter in the seismic band because of a lower noise level, whereas the reverse is true in the subseismic band. The poorer quality of the gravimeter record in the seismic band is probably due to site effects (sediments vs. bedrock) rather than of instrumental origin. In contrast, the higher noise level of the seismometer in the subseimic band is probably due to the temperature response of the instrument. It is expected that operating the STS-1 isothermally, or recording on-site temperature changes for correction will considerably improve its signal-to-noise ratio in the subseimic band. In comparison with recent mean models of high and low seismic background noise levels, both instruments nevertheless indicate low noise levels at all frequencies.

Interdigitated array microelectrodes as electrochemical sensors

We investigated electrochemical measurements with interdigitated array ( IDA) electrodes in both stationary solutions and flow systems. In a stationary solution, we achieved a very low detection limit of 10 pM of reversible redox species by using substitutional stripping voltammetry, which is a new type of stripping voltammetry using an IDA microelectrode. In flow systems, current enhancement by redox cycling is less effective than that in a stationary solution. The flow rate dependence of redox cycling is constant in the amperometric region, varies with coulometric yield in the quasi-amperometric region, and is inversely proportional to the 2/3 power of the volume flow rate in the coulometric region. A low detection limit of 5 fg (32 amol) is obtained for dopamine due to the high current density and low background noise level (0.1 pA) at the carbon-based IDA microelectrode used as a detector for liquid chromatography. A new separation approach is demonstrated which combines electrochemical detection and a molecular template. The electrode is first partly covered with print molecules and then modified with silane coupling reagent. The catechol-imprinted electrode shows the usual diffusion-limited cyclic voltammogram of catechol and has a diminished response against all catecholamines. The selectivity between catechol and epinephrine is about 100 when the electrode is used as an electrochemical detector in liquid chromatography.

Assessment of acoustical environments in malls in Saudi Arabia: A case study—Al-Rashid Mall

Most of the recently developed malls in Saudi Arabia have provided poor acoustical environments. Assessment of such environments is dis- cussed in detail in this paper through a case study; Al-Rashid Mall in Al-Khobar. Physical characteristics of the mall are described along with the special acoustical systems that are incorporated within the mall. One of these systems is the public address system which has many loudspeakers and feedback microphones that allow the system to automatically adjust the loudness of the sound signal produced according to the noise level. Unfortunately, this system has failed to provide the functions for which it was built. Acoustical characteristics such as background noise levels, reverberation time, and the sound transmission index (STI) were measured and analyzed in many locations. It was found that the mall has unexpectedly provided high background noise levels and reverberation time, as well as very poor speech intelligibility. Causes of such problems along with possible solutions are conceptually discussed. Finally, general social cultural factors that affect acoustical environments in malls in Saudi Arabia are briefly discussed along with a set of recommendations to overcome such factors.

Hybrid time-frequency adaptive filtering for the recovery of ventricular late potentials.

Ventricular late potentials are small ECG components that have significant diagnostic importance. Temporal averaging is used to recover these signals from high levels of background noise, but is not the optimum approach. A new form of hybrid time-frequency adaptive filtering is introduced that is based on signal division into a series of frequency bands. This technique is able to process the averaged data further and to reduce significantly the noise levels beyond that achieved by simple averaging. Examples of the processing are shown and its applicability is discussed.

Improved detection limit for catecholamines using liquid chromatography-electrochemistry with a carbon interdigitated array microelectrode.

The detection limit of catecholamines can be lowered by using a carbon-based interdigitated array (IDA) microelectrode as a detector for liquid chromatography (LC). The IDA electrode is more sensitive than conventional glassy carbon electrodes due to the high current density caused by radial diffusion at each microband, and redox cycling between two microband arrays. Since the number of redox cycles increases at lower flow-rates, the carbon IDA is particularly useful for microbore LC. In an LC system with a 1-mm microbore column and a carbon IDA electrode, the peak height of dopamine (DA) and DOPAC did not decrease with decreasing flow-rate because of this redox cycling. A low detection limit of 5 fg (32 amol) and 9.6 fg (57 amol) was obtained for DA and DOPAC due to the high current density and low background noise level (0.1 pA) at the carbon IDA electrode. The total charge generated by oxidizing DA at the anodic array was more than the value calculated by assuming that all the DA molecules were oxidized.

Subjective and objective parameters of sound within fabric structures

An investigation of acoustics in 15 circuses with fabric roofs has been carried out. Objective acoustical parameters (reverberation time, clarity C80, and others) have been measured and questionnaires from the audience in the circuses have been obtained. Features of circuses acoustics are the decrease in reverberation times at low frequencies, echo (in halls with impervious fabric roofs), and high levels of background noise. The background noise levels in circuses before a performance were equal LA=46–56 dBA. The questionnaire contained subjective acoustical attributes: Timbre, balance, reverberance, spaciousness, echo, loudness, clearness, audibility of background noise, background noise affect on speech legibility, and others. Average mark estimates and results of measured noise level in halls (LA) have been subjected to factor analysis. Three factors have been extracted that can be interpreted as (1) overall acoustical impression of the music sound in a circus, (2) disturbing influence of the background noise, and (3) clarity of music and speech sounding.

System noise as a signal source for impedance measurements on batteries connected to operating equipment

Alternating-current impedance measurements provide useful information about the characteristics of electrochemical systems, such as batteries, and are envisioned as the basis for indirect methods of determining battery capacity. Impedance measurements rely on recording the response of the battery to a controlled current or voltage test signal. However, this type of measurement can be difficult with large batteries connected to operating equipment. High background noise levels, caused by time-varying changes in the battery load, interfere with the impedance measurement. Instead of attempting to eliminate background noise, we have used the noise as a test signal, in conjunction with Fourier transform (FT) signal processing, The current and voltage passing through cells in an operating telecommunications lead/acid battery string were determined with a simple, three- terminal connection. Impedance calculations were performed with a commercial FT signal analyzer. The results indicate that completely passive (no externally applied test signal, and not requiring diconnection of the string) impedance measurements of batteries connected to operating equipment are feasible.

Receiver characteristics of laser altimeters with avalanche photodiodes

The receiver characteristics of a laser altimeter system containing an avalanche photodiode photodetector are analyzed using the Gaussian approximation, the saddlepoint approximation, and a nearly exact analysis. The last two methods are shown to yield very similar results except when the background noise is extremely low and the probability of false alarm is high. However, the Gaussian approximation method is shown to cause significant errors even under relatively high levels of background noise and received signal energy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Noise Levels And Hearing Protection Devices: Effect On Student Welding Performance

Recent researchers have shown that high levels of background noise have a detrimental effect on students’ abilities to perform learning tasks. Daniels (1985), Jewell (1977, 1978), and HambrickDixon found that high noise levels produced a detrimental effect on students’ abilities to perform cognitive or psychomotor skills. Jewel1 (1977, 1978) also discovered that students exposed to higher levels of sound required more time to complete assigned tasks. Another area of concern is the effect of impact or impulse noise. Research has shown that sudden impact noise (such as welding metal dropped on a concrete floor) or impulse noise (a grinding wheel intermittently coming in contact with steel) can cause actual damage to parts of the inner ear (Bohne, 1976; Luz & Hodge, 1971). Depending on the decibel level, impact or impulse noise levels can cause temporary loss of hearing activity or even result in damage that is permanent. The use of hearing protective devices (HPD’s) has been established as a sound practice to reduce the negative effect of loud noise on students’ performance levels (Feldman and Grimes, 1985; Hartley, 1974; Miller, 1986). Experimental research (Miller, 1986) has shown that HPD’s areeffective in maintaining higher levels of student performance when completing learning activities under noisy conditions. Standard maximum levels of noise exposure have been established by the Occupational Safety and Health Administration (OSHA, 1981). The maximum exposure levels and time periods during a working day without hearing protection are shown in Table 1. More recent federal regulations (OSHA, 1981) are imposing a maximum eight hour exposure limit of 85 decibels as the point where employers are required to monitor noise levels, notify employees, and recommend use of HPD’s. At noise levels of 90 decibels and above, employees are required to use HPD’s. Table 1 Permissible Exposure Time by Intensitv of Sound Pressure Level in Decibels (dBA)

Real-time portable multi-layer perceptron voice fundamental-period extractor for hearing aids and cochlear implants

Previous work has shown that it is possible to train a multi-layer perceptron to estimate the voice fundamental period ( Tx) for multiple speakers in the presence of high levels of background noise. The algorithm has been implemented in real-time on a TMS320C25 based development system. A prototype pocket-sized portable device has been constructed and the real-time software transferred to it. This will provide the basis for a new generation of signal processing hearing aids for the profoundly and totally deaf. Power supply current is sufficiently low for battery operation for periods of 12 hours between charges. The basic algorithm has been adapted to provide the higher time resolution which will make it applicable to a wide range of other applications.

Spatially mediated release from auditory masking in an anuran amphibian

Summary. 1. The acoustic environment in which many species of frogs must communicate is characterized by high levels of background noise. Because the anuran auditory system is directionally sensitive, spatial cues should be useful in enhancing the ability of these animals to detect and localize calling conspecifics under such conditions. 2. We presented female green treefrogs, Hyla cinerea, with synthetic conspecific advertisement and aggressive calls in the presence of background broadband noise to assess the importance of directional information in signal detection, discrimination and localization. 3. We found that angular separation of call and noise sources facilitated a release from masking; females which failed to orient towards and approach speakers broadcasting calls positioned adjacent to a noise source did so when the noise sources were separated from the speakers by 45 ~ or 90 ~ . We estimate the improvement in signal-to-noise ratio with separation to be 3 dB or less. This increase was insufficient to facilitate discrimination between advertisement and aggressive calls.

Field Operated Seismograph with Analog Recording and Short Seismic Telelink

The paper highlights in brief the characteristics of seismic waves generated due to earthquakes. The design parameters of seismograph for recording and processing seismic signals, have been discussed. Design details of a field-operated analog seismograph have been described. A new technique for synchronization of seismic clock with ATA signal has been illustrated. In order to improve upon the seismic signal recording in presence of high level background noise, a short seismic telelink between the seismometer and recorder, has been proposed. On the basis of results obtained with the present instrument, suggestions have been made to incorporate some new design features to enhance its capabilities further.

Review of ISO and ANSI standards for the determination of sound power levels of noise sources using sound intensity measurements

Sound intensity measurements can now be used to determine accurately the in situ sound power of machinery noise sources in the presence of high levels of background noise. Meetings of working group ISO/TC43/SC1/WG25 began in 1982 and a first draft standard was produced in late 1985. Meetings of working group ANSI S12-21 began in 1983 and produced first draft of a standard in 1984. The ANSI draft standard was circulated for balloting as a standard in 1987, and the ISO third draft was circulated in 1988. Although the ISO and ANSI drafts are similar, there are some differences. The ISO draft allows precision, engineering, and survey grade determinations and requires four indicators to be measured to decide the grade achieved. The ANSI draft only allows engineering determinations of sound power. The ISO draft only allows fixed point measurements, while the ANSI draft allows either fixed point or scanning measurements of intensity on a surface enclosing the source. Last year, 17 laboratories in North America took part in a round robin using the ANSI draft.

Auditory‐nerve representation of communication signals in background noise

Anuran auditory‐nerve fibers phase‐lock to the periodicity of complex acoustic signals, even though many of these fibers do not synchronize to pure tones at their best frequencies (BFs). In this experiment, the effects of background masking noise on peripheral coding of both spectral and temporal structure of the male bullfrog's species‐specific advertisement call was examined. Synthetic advertisement calls with 21 components (periodicity of 100 Hz) were digitally constructed and presented via a closed‐field system against different levels of noise. Plots of average discharge rate versus BF show peaks corresponding to the periodicity and low‐frequency spectral energy in the signal when presented at noise levels near threshold. These profiles change substantially in the presence of high levels of background noise. Plots of average localized synchronized rate (ALSR) against BF are much less influenced by noise. The data suggest that temporal coding of this natural call is more resistant to noise masking than is a representation based solely on discharge rate. [Work supported by NIH.]