• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.39-45
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• 2018

Compressive sensing allows recovering an original signal which has a small dimension of the signal compared to the dimension of the entire signal in a short period of time through a small number of observations. In this paper, we proposed a method for detecting tonal signal which caused by the machinery component of a vessel such as an engine, gearbox, and support elements. The tonal signal can be modeled as the sparse signal in the frequency domain when it compares to whole spectrum range. Thus, the target tonal signal can be estimated by S-OMP (Simultaneous-Orthogonal Matching Pursuit) which is one of the sparse signal recovery algorithms. In simulation section, we showed that S-OMP algorithm estimated more precise frequencies than the conventional FFT (Fast Fourier Transform) thresholding algorithm in low SNR (Signal to Noise Ratio) region.

• International conference on construction engineering and project management
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• 2022.06a
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• pp.912-919
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• 2022

The study is an image-based assessment that uses image processing techniques to determine the condition of concrete with surface cracks. The preparations of the dataset include resizing and image filtering to ensure statistical homogeneity and noise reduction. The image dataset is then segmented, making it more suited for extracting important features and easier to evaluate. The image is transformed into grayscale which removes the hue and saturation but retains the luminance. To create a clean edge map, the edge detection process is utilized to extract the major edge features of the image. The Otsu method is used to minimize intraclass variation between black and white pixels. Additionally, the median filter was employed to reduce noise while keeping the borders of the image. Image processing techniques are used to enhance the significant features of the concrete image, especially the defects. In this study, the tonal zones of the histogram and its properties are used to analyze the condition of the concrete. By examining the histogram, the viewer will be able to determine the information on the image through the number of pixels associated and each tonal characteristic on a graph. The features of the five tonal zones of the histogram which implies the qualities of the concrete image may be evaluated based on the quality of the contrast, brightness, highlights, shadow spikes, or the condition of the shadow region that corresponds to the foreground.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.348-353
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• 2012

This paper presents the HRTF based experimental approach to figure out why the human auditory perception on the interior noise source including the directional tonal components does not well match with the dominant features extracted from recorded acoustic signals in terms of psycho-acoustics. Since the general objective evaluation models for tonalness among various sound attributes are a function of width, frequency, excessive level of tonal components respectively, the directional tonal components cannot be properly evaluated without considering the effects of head-related transfer function on the binaural auditory perception. Thus, the directivity of source is additionally considered to prevent the erroneous conclusions from the same sound source in the process of source identification. The signal synthesis technique is used to solve a little difficulty in measuring all of desired acoustic signals for jury evaluation. The sound attributes of synthetic acoustics signals are analyzed to roughly predict the results of jury evaluation in advance by using sound quality factors such as loudness, sharpness, roughness, fluctuation strength and tonality. The jury evaluation is carefully conducted based on the recommended guideline suggested by N. Ottoet al. Each sound is respectively evaluated by selecting a value between -2 and 2 in intervals of 0.2 point. Through above procedure, based on the results of jury evaluation, it is confirmed that serious problems can be caused in the process of analyzing the dominant sound attributes in terms of psycho-acoustics according to the type of a microphone and a playback system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.6
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• pp.460-466
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• 2003

The aeroacoustic characteristics and noise reduction method of a centrifugal fan for a bagless vacuum cleaner were studied. The major noise source of vacuum cleaner is the centrifugal fan. The impeller of the fan rotates over 30000 rpm and generates very high-level piercing noise. It was found that the dominant noise source of the fan is generated from the aerodynamic interaction between the highly rotating impeller and stationary diffuser. In order to reduce the high tonal sound generated from the aerodynamic interaction between the impeller and diffuser, tapered impeller was carefully designed and tested. The trailing edge of the tapered impeller was inclined and this reduces the flow interactions between the rotating impeller and the stationary diffuser because of some phase shift. The static efficiency of the new impeller is slightly lower than the conventional one. The overall SPL is reduced about 3.6 dBA. The SPL of blade passing frequency(BPF) is reduced about 6 dBA and the $2^{nd}$ BPF is reduced about 20 dBA. The vacuum cleaner with the tapered impeller has lower noise level than that of the previous impeller and the strong tonal sound was dramatically reduced.

• The Journal of the Acoustical Society of Korea
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• v.31 no.6
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• pp.384-390
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• 2012

Passive sonars employ DEMON(Detection of Envelope Modulation on Noise) processing to extract propeller information from the radiated noise of underwater targets. However, the conventional DEMON processing suffers from the interference of tonal signals because it extracts propeller signals and some types of tonal signals as well. If there are some tonals in the frequency band for DEMON processing, the conventional DEMON processing may additionally extract frequency informations originated from the interaction between different tonals. In this paper, we propose a modified DEMON processing, which can eliminate the interference of the tonals. The proposed algorithm removes tonals in DEMON processing band before demodulation processing, hence results the robustness to the interference of the tonals. Some numerical simulations demonstrate the improved performance of the proposed algorithm against the conventional algorithm.

• The KSFM Journal of Fluid Machinery
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• v.7 no.1 s.22
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• pp.17-23
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• 2004

Aeroacoustic characteristics of sirocco fan used in Over-The-Range (OTR) has been analyzed in this paper. A microwave hood combination over the gas range is short for the OTR. The flow phenomena of the double-sided sirocco fan was analyzed numerically and experimentally by using commercial code and three dimensional PIV for flow visualization. Also, microphone array is used in order to understand acoustic characteristics of OTR. Two dimensional unsteady flow and acoustic simulation is tried to qualitatively estimate the effects of tonal noise and broadband noise on the overall sound pressure level. It is found that tonal sound is generated from the strong interaction between the impeller and cutoff while broadband sound is generated from the strong secondary flows along the scroll surface. To reduce the noise level, the V-shape cut-off was applied to improve the sound quality by reducing tonal noise. So the peak noise at BPF (Blade Passing Frequency) was almost reduced. The shape of flow-guide to suppress the secondary flow over the scroll surface was carefully checked. It is found that this affects flow pattern at the fan exit and reduces the broad band noise. Through this numerical and experimental study, the sound pressure level was lowered by 4dBA compared to that of the previous fan at the operating point.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.10
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• pp.692-699
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• 2015

Buffeting noise through a rear window in an automobile is investigated by using lattice Boltzmann method. The generation mechanism of the buffeting noise can be understood as the resonance mechanism in a Helmholtz resonator, which is driven by the convecting vortex in a shear-layer flow over the neck of the resonator. Two methods to suppress the buffeting noise are proposed, and their effects are quantitatively assessed. Opening front window reduces the observed buffeting tonal noise by 25 dB and the overall SPL by 4 dB, and the installation of a Helmholtz resonator acting as a dynamic damper reduces the tonal component that by 35 dB and the overall SPL by 10 dB.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1869-1874
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• 2004

Acoustic pressure field around the cross-flow fan is predicted by a hydrodynamic-acoustic splitting method. Unsteady flow field is obtained by solving the incompressible Navier-Stokes equations using an unstructured finite-volume method on the triangular meshes, while the acoustic waves generated inside the cross-flow fan are predicted by solving the perturbed compressible equations(PCE) with a 6th-order compact finite difference method. Computational results show that the acoustic waves of BPF tone are generated by interactions of the blades wakes with the stabilizer, which then are reflected from the rear-guider and mainly propagate towards the fan inlet. Also, a directivity of BPF noise predicted by the PCE is noticeably different from that of the FW-H equations, in which a fan casing effect cannot be included.

• The Journal of the Acoustical Society of Korea
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• v.22 no.5
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• pp.367-374
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• 2003

In this paper, we propose an audio watermarking method using the attribute of tonal masker. First, the attribute of tonal masker as an audio watermarking attribute is analyzed. According to existing researches, it is possible to be imperceptible modulation for the energies of the frequencies that compose a tonal masker. And when the relation between the tone energy and the left or right frequency energy after various signal processing is compared with the one before the processing, very few changes are showed. We propose an audio watermarking method using these attributes of tonal masker. A watermark bit is embedded by the modulation of the difference between the two neighboring frequency energies of a tone. In the detection, the modulated the tonal masker is searched using the key wed in the embedding without original audio and the embedded watermark bit is detected. After each attack of noise insertion, band-pass filtering, re-sampling, compression, echo transform and equalization, the detection error ratios of the proposed method were average 0.11%, 1.26% for Classics and Pops. And the SDG(Subjective Diff-Grades) scale evaluation of the sound quality of the watermarked audio result in the average SDG -0.31.

• The Journal of the Acoustical Society of Korea
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• v.12 no.4
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• pp.14-20
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• 1993

본 논문에서는 주변 소음을 감소시키고 표적원의 방사음으로부터 tonal 성분을 추출하기 위한 방법으로서 잡음 정규화 기법에 대하여 연구하였다. 지금까지 알려진 기법들을 정리하였으며, ATW, 최빈치 필터등의 새로운 기법을 도입, 적용하여 그 성능을 평가하였다. 그리고 tonal 성분을 검출하기 위한 임계값 결정을 위해 오경보확률과 검출확률을 시뮬레이션을 통해 구하였다.