High-frequency Noise Reduction Research Articles

Evaluation of the attenuation mechanism of the noise reduction performance of polyurethane porous elastic road surface

The polyurethane porous elastic road surface (PERS) demonstrates superior noise reduction performance, primarily due to its porous structure that facilitates effective sound absorption and its high elasticity that contributes to substantial vibration attenuation. However, it is susceptible to void clogging and long-term aging during service, leading to a gradual decline in noise reduction performance. To investigate the attenuation characteristics of noise reduction performance in PERS mixtures under void clogging and long-term aging conditions, this study investigated PERS mixtures subjected to various clogging cycles and aging times. Concurrently, the tire vertical drop test and standing wave tube absorption coefficient test were employed to analyze the variation rule in the noise sound pressure level (SPL) and sound absorption coefficient frequency curves under the above conditions. The results show that the noise reduction performance of the PERS mixture exhibits a variation rule of first decreasing and then increasing with the increase of the clogging cycles, and the required clogging amount to reach the void saturation state is 30–40 g. Compared to before clogging, the PERS mixture after clogging has an enhanced ability to absorb low-frequency noise and a weakened ability to absorb high-frequency noise; the sizes of the cloggings have a higher degree of attenuation in low-frequency sound absorption than in high-frequency. As long-term aging progresses, the noise reduction performance of the PERS mixture first increases and then decreases. Notably, long-term aging predominantly impacts the high-frequency noise reduction capabilities of the PERS mixture. The impact of void clogging on the noise reduction performance of PERS mixtures is found to be more pronounced than that of long-term aging.

An adaptive fully convolutional network for bearing fault diagnosis under noisy environments.

Intelligent diagnostic algorithms based on convolutional neural networks (CNNs) have shown great potential in diagnosing various conditions. However, accurately and robustly diagnosing faults in noisy situations remains challenging. This study presents an adaptive fully convolutional network (AFCN) for identifying bearing defects in noisy environments. First, we use a novel large kernel convolution method for high-frequency noise reduction and wide-area temporal feature extraction. By utilizing a sequence of stacked residual adaptive convolution blocks, the AFCN achieves a selective emphasis on significant features and adaptive adjustment of feature weights at various convolution scales. The experimental results have shown that the AFCN achieves a diagnostic accuracy of over 90% for the faults in the CWRU dataset under the -8 dB noise and over 77% for the PU dataset in the case of -6 dB noise. The comparison results with five advanced baseline models have demonstrated the superiority of the AFCN in feature extraction, noise immunity, and robustness to the noise environment. The AFCN provides a better adaption to noise interference than conventional CNNs and other advanced adaptive networks.

Tuning the acoustic characteristics of bottle plant garden

This work presents a finite element study to compute the acoustic performance of a garden that consists of periodically arranged bottle plants. The purpose of this work is to achieve low- and high-frequency noise reduction using plastic waste bottles. A harmonic excitation is given at one end, and transmission loss is calculated as a function of frequency between the two ends of the computational domain. The result shows that bottle plants produce a high-frequency wide band (1300–2100 Hz) around Bragg's frequency as well as a low-frequency sharp narrow band at the resonance frequency (∼305 Hz) of the bottle. To achieve a wider band gap at low frequencies, water level in the bottles is kept at different levels. The result showed that placing bottles with various water levels next to one another causes a bigger band gap at low frequencies (255–360 Hz). As a result, the low-frequency band gap can be tuned by changing the water level in the bottles. Plants' ability to absorb sound further dampens it at specific frequencies. Utilizing the plastic bottle to form such a garden has a major environmental impact and can function as a visually pleasing area while promoting calm and tranquilly.

High frequency noise reduction in ECG signal by adaptive filter using FxLMS algorithm

High frequency noise reduction in ECG signal by adaptive filter using FxLMS algorithm

Thresholding Methods for Reduction in Data Processing Errors in the Laser-Textured Surface Topography Measurements.

There are many factors influencing the accuracy of surface topography measurement results: one of them is the vibrations caused by the high-frequency noise occurrence. It is extremely difficult to extract results defined as noise from the real measured data, especially the application of various methods requiring skilled users and, additionally, the improper use of software may cause errors in the data processing. Accordingly, various thresholding methods for the minimization of errors in the raw surface topography data processing were proposed and compared with commonly used (available in the commercial software) techniques. Applied procedures were used for the minimization of errors in the surface topography parameters (from ISO 25178 standard) calculation after the removal and reduction, respectively, of the high-frequency noise (S-filter). Methods were applied for analysis of the laser-textured surfaces with a comparison of many regular methods, proposed previously in the commercial measuring equipment. It was found that the application of commonly used algorithms can be suitable for the processing of the measured data when selected procedures are provided. Moreover, errors in both the measurement process and the data processing can be reduced when thresholding methods support regular algorithms and procedures. From applied, commonly used methods (regular Gaussian regression filter, robust Gaussian regression filter, spline filter and fast Fourier transform filter), the most encouraging results were obtained for high-frequency noise reduction in laser-textured details when the fast Fourier transform filter was supported by a thresholding approach.

The unsupervised pattern recognition for the ECG signal features detection

Smart devices and cloud-based technologies allow continuous non-invasive bio-signal recordings in daily life activities. There are many programs and applications that allow monitoring health condition and sharing that information with other people. However, bio-signals that are recorded in real nonstationary conditions are highly contaminated with noise that depends on various activities. Improper signal processing algorithms may lead to a faulty diagnosis or inaccurate decision-making results. Movement contaminated bio-signals require adaptive filtering and feature extraction algorithms because low frequency trends are mostly unstable, and the noise may cause higher impulses than the signal itself. That is why ordinary ECG signal parameters extraction algorithms fail in real time signal processing. In this research signals were filtered using two different methods: Butterworth filter for the high frequency noise reduction and BEADS algorithm for the low frequency noise removal. A new ECG feature extraction algorithm was proposed that is based on the unsupervised MTEO algorithm together with additional local extremum search. The proposed algorithm was compared with other methods on the MIT-BIH database. The additional comparison was made with Pan-Tompkins and k-TEO algorithms on ECG signals that were recorded in movement. Several examples are presented that show how each algorithm performs during training sessions with various intensity levels. The suggested method performed in linear time complexity that made it sufficient for the real time data processing. The obtained ECG parameter values could be used for diagnostics and fatigue recognition in health monitoring processes.

High-Frequency Noise Reduction in Mechanical Compartment of a Household Refrigerator via Dynamic Absorber Design

This study presents a method to reduce high-frequency sound emitted from the mechanical compartment of a household refrigerator. The noise was found to be generated due to the structural vibration of the discharge cover attached to a linear compressor in the mechanical compartment. Based on the vibration characteristics of the conventional discharge cover, a dynamic absorber, which will be combined with the discharge cover, was designed for use in absorbing high-frequency noise in the discharge cover. Product testing for a refrigerator equipped with the modified discharge cover (which has the dynamic absorber) was performed to see if the enhanced discharge cover is useful to reduce the high-frequency sound under consideration. From noise level measurement results, it is observed that 2.5 and 1.7 dB of noise reduction effects on the front and rear sides of the refrigerator are made. Furthermore, it is found that noise in the range of 2800–3550 Hz, where the target frequency of dynamic absorber is included, is reduced. Finally, one can see the feasibility of the proposed method, and it is proven one of the viable solutions to the noise reduction issues in the household refrigerators.

Reconfigurable Architecture for Multi-lead ECG Signal Compression with High-frequency Noise Reduction

Electrocardiogram (ECG) is a record of the heart’s electrical activity over a specified period, and it is the most popular noninvasive diagnostic test to identify several cardiac diseases. It is an integral part of a typical eHealth system, where the ECG signals are often needed to be compressed for long term data recording and remote transmission. Reconfigurable architecture offers high-speed parallel computation unit, particularly the Field Programmable Gate Array (FPGA) along with adaptable software features. Hence, this type of design is suitable for multi-channel signal processing units like ECGs, which usually require precise real-time computation. This paper presents a reconfigurable signal processing unit which is implemented in ZedBoard- a development board for Xilinx Zynq −7000 SoC. The compression algorithm is based on Fast Fourier Transformation. The implemented system can work in real-time and achieve a maximum 90% compression rate without any significant signal distortion (i.e., less than 9% normalized percentage of root-mean-square deviation). This compression rate is 5% higher than the state-of-the-art hardware implementation. Additionally, this algorithm has an inherent capability of high-frequency noise reduction, which makes it unique in this field. The confirmatory analysis is done using six databases from the PhysioNet databank to compare and validate the effectiveness of the proposed system.

Low-Noise Broadband CMOS TIA Based on Multi-Stage Stagger-Tuned Amplifier for High-Speed High-Sensitivity Optical Communication

Constrained by the transimpedance limit, the conventional 1-stage shunt-feedback transimpedance amplifier (1S-SF-TIA) suffers poor noise and gain at higher data rates. In this paper, we propose to use a multi-stage stagger-tuned amplifier (MSTA) to constitute TIA (MSTA-TIA), which not only transcends the transimpedance limit of 1S-SF-TIA, but also realizes noise reduction in multiple fronts. First, the high-gain MSTA enables 17X TIA gain over 1S-SF-TIA, which effectively suppresses the white noise. Second, the MSTA realizes at least 2.8X~1.6 lower noise than the conventional multi-stage amplifier, which is essential to form low-noise TIA since the amplifier noise usually dominates. Third, the TIA built upon the 3-stage STA also shows steeper out-of-band roll-off to enable high-frequency noise reduction. Overall, the MSTA-TIA achieves 6.9X and 1.9X noise power reduction over conventional single-stage and multi-stage SF-TIAs. As a demonstration, a 10 Gb/s optical receiver front-end prototype employing proposed MSTA-TIA topology is implemented in a standard $0.18~\mu \text{m}$ CMOS technology. It achieves transimpedance gain of 68.3dB $\Omega $ , electrical bandwidth of 8.5GHz, and excellent input-referred noise current of $0.97~\mu $ Arms. The chip occupies 0.78 mm2 while consuming 43 mA from 1.8 V power supply. The low-noise design methodology in this paper empowers mature CMOS to compete with SiGe to make low-noise high-gain optical IC.

A hybrid approach to active and passive noise control for open windows

This research focuses on the use of an open window with an active noise control (ANC) system and a splitter silencer to improve the attenuation level of broadband noise. We previously introduced a similar idea with a splitter silencer and a loudspeaker inside a duct. However, it is challenging to achieve noise reduction with a splitter silencer in a short duct. In our previous research, we achieved noise reduction at an open window with an array of ANC units, in which a reference microphone with a loudspeaker is collocated. However, this system had limited high-frequency noise reduction due to the distance between each loudspeaker. Here, we improved noise reduction by integrating a collocated ANC system and a splitter silencer, which has an open ratio of 50%. Each unit has a reference microphone at the front and a loudspeaker at the back, which generate anti-noise. Four units are combined in an array with a splitter silencer. In an experiment, we implemented two splitter silencers in an eight-channel ANC system at an open window (24 × 48 × 12 cm). The results show that the splitter silencers attenuated high-frequency noise above 2 kHz. Moreover, the ANC system achieved an attenuation of 2 to 10 dB for noise in the range of 200 Hz to 2 kHz. Overall, we were able to achieve a total attenuation of 2 to 17 dB above 200 Hz.

On the universal trends in the noise reduction due to wavy leading edges in aerofoil–vortex interaction

Existing studies suggest that wavy leading edges (WLEs) offer substantial reduction of broadband noise generated by an aerofoil undergoing upstream vortical disturbances. In this context, there are two universal trends in the frequency spectra of the noise reduction which have been observed and reported to date: (i) no significant reduction at low frequencies followed by (ii) a rapid growth of the noise reduction that persists in the medium-to-high frequency range. These trends are known to be insensitive to the aerofoil type and flow condition used. This paper aims to provide comprehensive understandings as to how these universal trends are formed and what the major drivers are. The current work is based on very-high-resolution numerical simulations of a semi-infinite flat-plate aerofoil impinged by a prescribed divergence-free vortex in an inviscid base flow at zero incidence angle, continued from recent work by the authors (Turner & Kim, J. Fluid Mech., vol. 811, 2017, pp. 582–611). One of the most significant findings in the current work is that the noise source distribution on the aerofoil surface becomes entirely two-dimensional (highly non-uniform in the spanwise direction as well as streamwise) at high frequencies when the WLE is involved. Also, the sources downstream of the LE make crucial contributions to creating the universal trends across all frequencies. These findings contradict the conventional LE-focused one-dimensional source analysis that has widely been accepted for all frequencies. The current study suggests that the universal trends in the noise-reduction spectra can be properly understood by taking the downstream source contributions into account, in terms of both magnitude and phase variations. After including the downstream sources, it is shown in this paper that the first universal trend is due to the conservation of total (surface integrated) source energy at low frequencies. The surface-integrated source magnitude that decreases faster with the WLE correlates very well with the noise-reduction spectrum at medium frequencies. In the meantime, the high-frequency noise reduction is driven almost entirely by destructive phase interference that increases rapidly and consistently with frequency, explaining the second universal trend.

Effects of complex graphite-like carbon coating on gear vibration noise

Abstract In this paper, the effects of substrate surface roughness and the addition of yttrium, cerium and tantalum on thickness uniformity of graphite-like carbon (GLC) coatings on gears were studied by magnetron sputtering method using mosaic targets. And noise reduction effects of gear pump deposited with complex GLC coatings were evaluated at different rotate speeds. The results showed that target-substrate distance, sputtering angle and surface roughness had influences on thickness uniformity of GLC coatings on gear. The introduction of elements Y, Ce and Ta into GLC coatings could effectively improve their thickness uniformity. The complex GLC coating with optimal thickness uniformity on gear exhibited significantly reduction effect for gear noise and the reduction effect for axial vibration was better than that of radial vibrations. Compared with uncoated gears, the noise for the coated gears was decreased by 10 dB at 2000 rpm. Good high-frequency noise reduction was obtained, which could be decreased by 19 dB in the range of 4000–10,000 Hz.

Numerical investigation of low-noise airfoils inspired by the down coat of owls

Numerical analysis of airfoil geometries inspired by the down coat of the night owl is presented. The bioinspired geometry consists of an array of ‘finlet fences’, which is placed near the trailing edge of the baseline (NACA 0012) airfoil. Two fences with maximum nondimensional heights, and are investigated, where is the displacement thickness at 2.9% chord upstream of the airfoil trailing edge. Wall-resolved large eddy simulations are performed at chord-based Reynolds number, , flow Mach number, , and angle of attack, . The simulation results show significant reductions in unsteady surface pressure and farfield radiated noise with the fences, in agreement with the measurements available in the literature. Analysis of the results reveals that the fences increase the distance between the boundary layer turbulence (source) and the airfoil trailing (scattering) edge, which is identified to be the mechanism behind high-frequency noise reduction. These reductions are larger for the taller fence as the source-scattering edge separation is greater. Two-point correlations show that the fences reduce the spanwise coherence at low frequencies for separation distances greater than a fence pitch (distance between two adjacent fences) and increase the coherence for smaller distances, the increase being higher for the taller fence. This increase in coherence and the reduced obliqueness of the leading edge of the fence are hypothesized to be responsible for the small increase in farfield noise at low frequencies observed in the simulations with the taller fence.

Integrated psychoacoustic active noise control and masking

The active noise control (ANC) algorithms are widely applied in noise-canceling headphones. However, the disadvantage of conventional ANC algorithms is the high computational cost from high order finite-impulse-response filter, which also leads to slower convergence. Subband ANC algorithms, which are based on the subband adaptive filter, are used to reduce computational complexity and to increase convergence rate. Moreover, noise cancellation performance decreases at the higher frequency due to the decreasing control zone. In headphones based application, perceptual quality of noise attenuation and target audio signal are important factors, and ANC algorithm must be designed to account for the psychoacoustic parameters. In this paper, we propose a new noise reduction approach in order to solve some existing ANC headphones problems, especially high-frequency noise reduction and perceptual quality of the playback sound. The proposed algorithm is a new approach of integrated psychoacoustic subband ANC and psychoacoustic masking. Psychoacoustic subband ANC achieves lesser computational cost than conventional subband ANC by using the psychoacoustic model to attenuate only audible noise components during music playback in the headphones. Proposed new integrated system is efficient for broadband noise attenuation. Psychoacoustic ANC reduces noise in the most sensitive frequency range for human’s hearing system, 0–4000 Hz, and masking operates in order to mask out residual and high-frequency noise. In additional, proposed noise reduction system reduces only audible noise components. The integrated ANC-masking system applied psychoacoustic analysis without producing artificial distortions to the music signal. Objective and subjective perceptual tests are evaluated for the proposed ANC-masking system with other subband ANC and masking algorithms. Results show the advantage of the proposed integrated system in the terms of the perceptual sound quality and high-frequency noise reduction.

Wavelet-Based Adaptive Denoising and Baseline Correction for MALDI TOF MS

Proteomic profiling by MALDI TOF mass spectrometry (MS) is an effective method for identifying biomarkers from human serum/plasma, but the process is complicated by the presence of noise in the spectra. In MALDI TOF MS, the major noise source is chemical noise, which is defined as the interference from matrix material and its clusters. Because chemical noise is nonstationary and nonwhite, wavelet-based denoising is more effective than conventional noise reduction schemes based on Fourier analysis. However, current wavelet-based denoising methods for mass spectrometry do not fully consider the characteristics of chemical noise. In this article, we propose new wavelet-based high-frequency noise reduction and baseline correction methods that were designed based on the discrete stationary wavelet transform. The high-frequency noise reduction algorithm adaptively estimates the time-varying threshold for each frequency subband from multiple realizations of chemical noise and removes noise from mass spectra of samples using the estimated thresholds. The baseline correction algorithm computes the monotonically decreasing baseline in the highest approximation of the wavelet domain. The experimental results demonstrate that our algorithms effectively remove artifacts in mass spectra that are due to chemical noise while preserving informative features as compared to commonly used denoising methods.

Measurement of hearing protector insertion loss at ultrasonic frequencies

The preferred method for assessing the attenuation of hearing-protective devices (HPDs) involves real ear attenuation at threshold (REAT) determinations, usually obtained in accordance with ANSI Standard S12.6-1997 or ISO Standard 4869-1, where measurements are normally made in the range 125–8000 Hz. In certain circumstances, the use of an acoustic test fixture (ATF) with built-in artificial ears is an acceptable substitute for subjective testing. In this case, the metric obtained is “insertion loss”; the difference between the open-ear and occluded-ear sound levels measured using the ATF microphone. REAT attenuations are not generally interchangeable with insertion loss measurements; however, their similarity often promotes data comparison. Experience has shown that subjective thresholds obtained above 8000 Hz are highly variable due primarily to decreased hearing sensitivity and to the complexity of high-frequency wave patterns. With an ATF, measurements may be carried out over an extended frequency range while minimizing the problems associated with subjective evaluations. In this study, the high-frequency insertion loss of two earmuff and three earplug HPDs was measured objectively at frequencies up to 22.4 kHz. One of the earplugs provided consistently better performance than the other devices for both grazing and direct sound incidence. In addition, two lightweight materials (copier paper and foamcore sheeting) were evaluated for high-frequency noise reduction when placed in the direct path between the sound source and the artificial ear of the ATF. Of these, the foamcore was the more effective barrier. ©

Study on the Reduction of High-Frequency Noise for an Accelerated Gear Pump.

Study on the Reduction of High-Frequency Noise for an Accelerated Gear Pump.

Nylon impression fabric—acoustical application

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Optimum conditions for the high frequency noise reduction method in optical videodisc players

In a previous paper, the authors demonstrated the usefulness of the high frequency (HF) current superposition noise reduction method. This paper discusses optimum conditions for the HF method. The main results obtained are that modulation current frequency must be higher than 600 MHz and modulation depth must be >120%. The optical path length between laser and disk and the removal for interference in the signal detectors must also be taken into consideration.