• Transactions on Electrical and Electronic Materials
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• 제15권4호
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• pp.182-188
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• 2014

When the windowed DFT algorithm is applied in harmonic measurements, the problem of initial-phase sensitivity will be encountered, this has an effect on harmonic amplitude accuracy. In this paper, the origin of initial-phase sensitivity is analyzed and the main factors that influence the level of initial-phase sensitivity are demonstrated. A method of reducing initial-phase sensitivity is proposed to increase the stability of harmonic measurements. We found that initial-phase sensitivity is determined by the side lobe peak level of the window functions when synchronous deviation is fixed. In addition, increasing the length of the time recorded can be used to remove initial-phase sensitivity. The correctness and validity of our conclusions have been confirmed through numerical results and field tests.

• 한국광학회:학술대회논문집
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• 한국광학회 2009년도 동계학술발표회 논문집
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• pp.123-124
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• 2009

• Journal of applied mathematics & informatics
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• 제20권1_2호
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• pp.17-34
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• 2006

Inverse coefficient identification problems associated with the fourth-order Sturm-Liouville operator in the steady state Euler-Bernoulli beam equation are investigated. Unlike previous studies in which spectral data are used as additional information, in this paper only boundary information is used, hence non-destructive tests can be employed in practical applications.

• 한국광학회:학술대회논문집
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• 한국광학회 2009년도 창립 20주년기념 특별학술발표회
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• pp.339-340
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• 2009

• 대한전자공학회논문지
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• 제26권9호
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• pp.1317-1321
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• 1989

The nonuniqueness of solutions to inverse scattering problems for the reconstruction of cross sectional permitivity distributions on dielectric cylinder is illustrated in view of numerical analysis based on the spectral inverse scattering scheme with the moment-method procedures. It is also shown that some additional treatmenents such as multiple measurements, various incidences, etc. are not effective to assure the uniqueness.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.122-126
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• 2002

Measuring color precisely requires the use of a colorimeter whose spectral response is as close as possible to the CIE response. Some techniques such as the NIST 4-color method can improve the precision. but under given conditions, the results can be worse.

• 한국해양공학회지
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• 제25권2호
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• pp.1-6
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• 2011

Vibration-based Structural Health Monitoring (SHM) systems use field measurements of operational signals, which are distorted by noise from many sources. Reducing this noise allows a more accurate assessment of the original "clean" signal and improves analysis results. The implementation of a noise reduction methodology for the Modal Distribution Method (MDM) is reported here. The spectral subtraction method is a popular broadband noise reduction technique used in speech signal processing. Its basic principle is to subtract the magnitude of the noise from the total noisy signal in the frequency domain. The underlying assumption of the method is that noise is additive and uncorrelated with the signal. In speech signal processing, noise can be measured when there is no signal. In the MDM, however, the magnitude of the noise profile can be estimated only from the magnitude of the Power Spectral Density (PSD) at higher frequencies than the frequency range of the true signal associated with structural vibrations under the additional assumption of white noise. The implementation of the spectral subtraction method to MDM may decrease the energy of the individual mode. In this work, a modification of the spectral subtraction method is introduced that enables the conservation of the energies of individual modes. The main difference is that any (negative) bars with a height below zero after subtraction are set to the absolute value of their height. Both noise reduction methods are implemented in the MDM, and an application example is presented that demonstrates its effectiveness when used with a signal corrupted by noise.

• 말소리와 음성과학
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• 제2권3호
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• pp.37-46
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• 2010

This study investigates acoustic characteristics of English and Korean voiceless sibilant fricatives as they appear before the three vowels, /i/, /$\alpha$/ and /u/. Three measurements - duration, center of gravity and major spectral peak - are employed to compare acoustic properties and vowel effect for each fricative sound. This study also investigates the question of whether Korean sibilant fricatives are acoustically similar to the English voiceless alveolar fricative /s/ or to the palato-alveolar /$\int$/. The results show that in the duration of frication noise, English /$\int$/ is the longest and Korean lax /s/ the shortest of the four sounds. It is also observed that English alveolar /s/ has the highest value, whereas Korean /s/ shows the lowest value in the frequency of center of gravity. In terms of major spectral peak, while English /s/ reveals the highest frequency, English /$\int$/ shows the lowest value. In addition, evidence indicates that there is a strong vowel effect in the fricative sounds of both languages, although the vowel effect patterns of the two languages are inconsistent. For instance, in the major spectral peak, both Korean lax /s/ and tense /$s^*$/ show significantly higher frequencies before the vowel /$\alpha$/ than before the other vowels, whereas both English /s/ and /$\int$/ exhibit significantly higher frequencies before the vowel /i/ than before the other vowels. These results indicate that Korean sibilant fricatives are acoustically distinct from both English /s/ and /$\int$/.

• 응용통계연구
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• 제21권3호
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• pp.547-560
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• 2008

스펙트럼 밀도함수(spectral density function)는 시계열 자료가 정상성(stationarity)을 만족하는 경우에 주파수 영역(frrqllrnFr domain)에서 시계열 자료의 자기공분산함수(auto-covariance function)을 결정짓는 함수이고, 평활된 주기도(smoothed periodogram)는 스펙트럼 밀도함수의 일치 추정량(consistent estimator)이 됨이 잘 알려져 있다. 본 연구에서는 시계열 자료를 평활된 주기도를 이용하여 군집화하는 방법을 소개한다. 최근 김희영과 박만식 (2007)의 연구에 의하면 이 거리는 정상시계열들을 효율적으로 분류하고 있음을 알 수 있다. 본 연구는 시계열 자료를 분류하는데 사용된 기존의 거리들을 간략히 소개하고, 우리나라 22개 지역에서 1987년 1월부터 2007년 12월까지 측정한 월별 강수량 자료를 대상으로 평활된 주기도 거리를 이용하여 지역을 군집화한다.

• 말소리와 음성과학
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• 제8권2호
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• pp.73-80
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• 2016

The purpose of this study was to analyze perceptual and spectral/cepstral measurements in patients with adductor spasmodic dysphonia(ADSD). Sixty participants with gender and age matched individuals(30 ADSD and 30 controls) were recorded in reading a sentence and sustained the vowel /a/. Acoustic data were analyzed acoustically by measuring CPP, L/H ratio, mean CPP F0 and CSID, and auditory-perceptual ratings were measured using GRBAS. The main results can be summarized as below: (a) the CSID for the connected speech was significantly higher than for the sustained vowel (b) the G, R and S for the connected speech were significantly higher than for the sustained vowel (c) Spectral/cepstral parameters were significantly correlated with the perceptual parameters, and (d) the ROC analysis showed that the threshold of 13.491 for the CSID achieved a good classification for ADSD, with 86.7% sensitivity and 96.7% specificity. Spectral and cepstral analysis for the connected speech is especially meaningful on cases where perceptual analysis and clinical evaluation alone are insufficient.