• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.122-125
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• 2011

In real environment, background noise exists everywhere and degrades the performance of system. To reduce this distortion, a speech enhancement algorithm can be very useful and variety methods have been proposed. In this paper, we propose a postfilter to improve the performance of optimally modified log-spectral amplitude (OM-LSA) estimator. Proposed algorithm uses the formant postfilter to minimize perceptual distortion caused by background noise. We adjust an emphasizing parameter which is varied by spectral flatness and first reflection coefficient. The performance of the proposed algorithm is evaluated by measuring the log-spectral distance (LSD) and the perceptual evaluation of speech quality (PESQ) score. The test results show the improvement of proposed algorithm compared to conventional OM-LSA.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.25-28
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• 2008

This study investigates the effect of geometrical shape of concert halls, with variation in the shape and location of diffusers. The acoustical characteristics both in the audience area and on the stage 1:50 scale models of shoebox and fan-shaped halls. It was found that the front side walls affect sound diffusion. The 1:50 scale model based on the Boston Symphony Hall was used for monaural impulse response measurements for calculation of RT, EDT, C80, G and ST1. In addition, calculating the numbers and amplitudes of reflection rays were applied to quantify diffusion phenomena.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.863-864
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• 2008

To predict the iris matching performance and guarantee its reliability, image quality measure prior to matching is desired. An analysis on iris image degradation factors which deteriorate matching performance is a basic step for iris image quality measure. We considered five degradation factors-white-out, black-out, noise, blur, and occlusion by specular reflection-which happen generally during the iris image acquisition process. Experimental results show that noise and white-out degraded the EER most significantly, while others on EER were either insignificant or degradation images resulted in even better performance in some cases of blur. This means that degradation factors that affect the performance can be different from those based on human perception or image degradation evaluation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.04a
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• pp.206-211
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• 1994

본 연구에서는 임의의 복소 음압 분포를 무한 평면에서 공간상의 Fourier 변환을 하여서 평면파 요소들의 중첩으로 해석하는 방법을 살펴보고 제한된 측정 조건에서 유발되는 문제들을 음원의 주파수에 대해서 모의 실험을 통하여 고찰해보았다. 실험으로는 단단한 시편(hard panel)과 스폰지(sponge)에 대해서 공간상의 fourier 변환을 통해 반사 계수를 얻고 수직입사에 대해 2-마이크로폰 방법으로 구한 반사계수와 비교하였다. 특히 다공성 물질인 스폰지에 대해서는 유동 저항을 측정하여 실험식으로부터 구한 반사 계수와의 비교를 하였으며 공간상의 음압 분포로부터 구한 반사계수에서 창문함수의 영향을 살펴보았다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.385-392
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• 2001

Time-dependent frequency and energy of free vibration of the Spagetti problem, that is the axially moving continuum with time-varying length, are investigated. Exact expressions for the natural frequency and time-varying vibration energy are derived by dealing with traveling waves. When the string length is increased, the vibration period increases, but the free vibration energy varies as a function of both translating velocity and boundary velocity of the continuum. However, when the string undergoes retraction, the vibration energy increases with time, String tension together with non-zero instantaneous velocity at the moving boundary results in energy variation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.6
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• pp.399-405
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• 2015

In this work we use the mode decomposition technique employing chirplet transform, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor. The mode decomposition technique is also used to estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize axial defects. The arrival times of the separated modes are calculated and the axial defect lengths can be evaluated by using the estimated arrival time. Results from an experiment on a carbon steel pipe are presented and it is shown that the accurate and quantitative defect characterization could become enabled using the proposed technique.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.457-467
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• 2004

Wave Transmission analysis is one of methods for power transmission and reflection coefficients in coupled infinite structures. This paper focuses the wave transmission analysis of point coupled structures among semi-infinite beams and infinite thin plates considering all kinds of waves. It is supposed that the junction through the beams and plates is an identical spot and no point of contact exist except the spot. The boundary conditions are applied at the spot for continuities of 6 DOF displacements and 6 DOF force equilibriums, and then wave fields are obtained in the coupled structures. Since wave components in plate field are simplified using asymptotic expressions of Henkel functions, the displacements and forces at the plate junction can be simply expressed with magnitudes of the wave components. The wave fields according to incident waves gives the power transmission coefficients in beam/plate point coupled structures. For both coupled structures with a beam vertically and obliquely joined to a plate, power transmission analysis is performed and the analysis results are compared and examined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.325-333
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• 2000

To predict vibrational energy density and intensity of partitioned complex system structures in medium-to-high frequency ranges, Power Flow Finite Element Method(PFFEM) programs for the plate elements are developed. The flexural, longitudinal and shear waves in plates are formulated and the joint element equations for multi-couped plates are fully developed. Also the wave transmission approach has been introduced to cover the energy transmission and reflection at the joint plate elements. Using the developed PFFEM program the energy density and intensity of the submarine and automobile shape structures are predicted with a harmonic point force at a single frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1900-1906
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• 2000

In this study, the vibration screening effectiveness of barriers which can isolate structures from ground-transmitted vibration generated by harmonic forces is performed. For high frequencies, the vibration screening effectiveness of barriers is analyzed from field tests, and compared with the results from numerical analyses using a commercial program, ANSYS. Using these numerical analysis procedures, the effectiveness for vibration with various low frequencies is predicted. The frequency analysis tests of surface waves are performed in order to estimate the dynamic material properties of soil for 100 Hz, 150 Hz, 200 Hz, and 250 Hz. Three-dimensional solid elements are used in order to consider the diffraction of waves in all directions. Spring-damper combination elements are used in order to avoid the reflection of waves on the boundary. The results of numerical analysis agree with those of field tests. From the results of this numerical analyses, the reduction of vibration for low frequencies induced by the traffic loads can be predicted.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.537-537
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• 2010

이 논문에서는 음향 임피던스를 제어하는 능동형 소음 제어 방법을 연구하였다. 관의 끝단에 스피커를 이용하여 음향 임피던스를 제어하게 된다. 음향 임피던스 제어는 음향의 반사를 최소화 하는 제어 방법을 이용하는 것으로, 닫힌 관의 끝단에 음파의 흡수와 반사를 제어한다. 나아가 음향 임피던스 제어 방법은 관의 중앙에 설치되어 적용된다. 이 경우에는 음향의 반사, 흡수 및 전달이 측정되고, 최소화하기 위한 임피던스가 계산된다. 이를 위해 가진기, 마이크로폰, 진동측정용 레이저 바이브로미터, 그리고 능동 소음 제어 하드웨어로 구성된 시스템을 구축하고 검증하였다.