• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.946-950
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• 2006

This paper proposed the ways for reduction of the prominent peak of the tone noise in air conditioning units. In order to find out the sources of the tone noise, the resonant frequencies and modes of the fans were investigated. Also, the effects of the ambient temperatures and material properties of the fans on the tone noise were studied. From the experiments, it was shown that the tone noise was greatly influenced by the torsional resonance of the fan and motor system and commutation frequency. In other words, the torsional resonance of the fan and motor system has not to be close to the commutation frequency (torque ripple frequency) which creates a rate of change in the angular acceleration in order to reduce the tone noise in air conditioning units.

• 한국통신학회논문지
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• 제15권10호
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• pp.797-810
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• 1990

The error rate equations of digitally modulated signals transmitted through the Gaussian noise and tone multiple interference channel have been derived. Using the derived equations of error probabilities in the environments of Gaussian noise tone interferer and Gaussian noise multiple interferer, the error rate performances of various digitally modulated signals have been evaluated, and compared in graphs as a function of average carrier to tone interferer power ratio(CIR), average carrier to multiple interferer power ratio(CIT) and the average carrer-to-Gaussian noise powr ratio(CIR). In this paper, the modulation schemes such as amplitude shift keying (ASK), phase shift keying(PSK), frequency shift keying(FSK), minimum shift keying(MSK), quadrature amplitud modulation(QAM) and amplitude phase shift keying(APK) have been selected for the study of performance comparison. The results of comparison show us that, in low bits/sec/Hz, PSK is superior to the other schemes, but in high bits/sec/Hz, mixed multi ary type is better than single multi ary type. And in strong noise evironment, the multiple interferer has much influence than tone interferer, however, in low noise environment. the mojor error factor is tone interferer. But tone interference effect nearly disappears over specified CIR level about 20[dB]. And the modulation schemes using amplitude are heavily influenced by multiple interference.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1288-1292
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• 2007

Mobile phone is necessary articles by increasing mobile communication now. People usually use the Mobile phone in any time and place. Ring tone of Mobile phone effect owner or other person. The sound level of Mobile phone ring tone could be considered as noise if it is too loud a specific situation. Manufacturing company improve ring tone of mobile phone better in consumer's perception. In this study, we record ring tone of mobile phone and estimated the complexity and nonlinear characteristics of the relation between subjective evaluation and sound metrics. Linear regression models were obtained for the subjective evaluation and sound quality metrics. Semantic Differential Method is used to study sound quality Evaluation. To analyze the sound quality of ring tone.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.229-229
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• 2006

WECPNL(Weighted Equivalent Continuous Perceived Noise Level) which designated currently in Domestic 'The Stanrd Method of Measuring Noise and Vibration' is composed of different factor with WECPNL that published in ICAO. Domestic WECPNL is concerned in application of $L_{MAX}$ measurement. On the other hand, ICAO's WECPNL is based on EPNL that includes factors of the pure tone correction and the duration time. NNI and NEF also are each based on PNL and EPNL. Because a military aircraft noise, especially, has the pure tone of high frequency and the irregular duration, it seems to be undesirable to estimate aircraft noise for using Domestic WECPNL. Therefore, this study was performed to detect a flaw of Korean WECPNL, through comparison of the trend of each other aircraft noise index by using equivalent rawdata.

• The Journal of the Acoustical Society of Korea
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• 제25권1E호
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• pp.32-35
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• 2006

The screech tone of underexpanded jet is numerically calculated without any specific modeling for the screech tone itself. Fourth-order optimized compact scheme and fourth-order Runge-Kutta method are used to solve the 2D axisymmetric Euler equation. Adaptive nonlinear artificial dissipation model and generalized characteristic boundary condition are also used. The screech tone, generated by a closed loop between instability waves and quasi-periodic shock cells at the near field, is reasonably analyzed with present numerical methods for the underexpanded jet having Mach number 1.13. First of all, the centerline mean pressure distribution is calculated and compared with experimental and other numerical results. The instantaneous density contour plot shows Mach waves due to mixing layer convecting supersonically, which propagate downstream. The pressure signal and its Fourier transform at upstream and downstream shows the directivity pattern of screech tone very clearly. Most of all, we can simulate the axisymmetric mode change of screech tone very precisely with present method. It can be concluded that the basic phenomenon of screech tone including the frequency can be calculated by using high-order and high-resolution schemes without any specific numerical modeling for screech tone feedback loop.

• 한국통신학회논문지
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• 제15권10호
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• pp.868-878
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• 1990

Upon introducing satellite communication system to Korea, one of the important problems to cope with is the effect from the probable intentional interference I.e. jamming. In this paper we have investigated how much the performance of ordinary PSK signal and Directed Sequence Spread Spectrum PSK signal degrade by the effect of jamming in the satellite communication system. In analysis we have consider the M ary PSK signal and the liniter type nonlinear satellite transponder in an environment of uplink tone or noise jamming plus Gaussian noise and downlink Gaussian noise. Using the derived error rate equation we have evaluated the error performance of BPSK and QPSK systems and compared this with that of DS BPSK system. Form the results, we know that the nonlinear satellite system is degraded more severely by the effect of noise jamming than tone jamming and the effect of tone jamming on the error rate performance can be reduced more remarkably by increasing the process gain in DS BPSK system rather than increasing carrier to jamming noise power ratio in conventional BPSK system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.2023-2028
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• 2004

The effects of nozzle-lip thickness on the relationship between screech tone and broadband shock-associated noise were experimentally investigated using a convergent-divergent nozzle with a design Mach number of 2.0. Overall sound pressure levels (OASPL) and noise spectra were obtained at far-field locations. Schlieren optical system was used to visualize the flow-fields of supersonic jets. A baffle plate was installed at the exit of the nozzle and its size was varied to obtain different nozzle-lip thicknesses. Experiment was carried out over a wide range of nozzle pressure ratios from 2.0 and 18.0, which corresponds to over- and under-expanded conditions. The results obtained clearly show that the screech tones are influenced by the nozzle-lip thickness. It is found that the screech tone and its peak amplitude are strongly dependent on whether the jet is over-expanded and under-expanded at the nozzle exit.

• 한국음향학회지
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• 제38권3호
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• pp.363-369
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• 2019

복잡한 회전 기계의 소음 상태 진단을 위한 다양한 연구가 수행되고 있다. 본 연구에서는 진동신호를 이용하여 블로워 모터의 효율적이고 객관적인 소음 상태진단을 위한 지수를 개발하였다. 블로워 모터의 이상 시 가장 흔히 나타나는 소음으로 틱/클릭 소음과 톤 소음이 있다. 발생 원인과 소음 특성에 따라 틱/클릭 소음의 상태 진단에는 시간-주파수 분석법을 그리고 톤 소음 상태 진단에는 주파수 영역에서의 평활화 기법을 이용하였다. 개발한 지수를 이용하여 블로워 모터의 소음 상태 진단을 수행하고 이를 전문가에 의한 진단 결과와 비교하였다. 그 결과 약 95 %의 일치율을 보였다.

• 한국음향학회지
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• 제24권1호
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• pp.43-51
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• 2005

본 논문에서는 잡음 에너지 제어를 통한 지각 필터의 성능을 향상시킴으로써 잡음에 의해 열화 된 오디오 신호의 음질을 개선하는 알고리즘을 제안한다. 기존의 방식에서는 묵음 구간에서 획득한 잡음 에너지를 사용하여 필터를 구성하여 사용하지만, 신호 구간마다 달라지는 신호의 세기 및 잡음의 환경 정도에 많은 영향을 받아 잡음의 에너지가 급격하게 변화한다면 음질의 개선률이 감소함을 알 수 있다. 그러나 제안하는 방식에서는 묵음 구간에서 추정한 잡음의 에너지 제어를 통해 초기 추정 잡음보다 가까운 추정 잡음을 얻음으로써 잡음 에너지가 급격하게 변화하여도 음질 개선률에는 변화가 적음을 알 수 있었다. 또한 저 대역에 영향을 미치는 잡음의 경우에도 다른 방법들과는 달리 음질의 개선이 뚜렷하였다. 기존 방식과의 비교를 위해 다양한 신호 대 잡음 비 (signal-to-noise ratio, SNR)에서 열화 된 오디오 신호를 입력으로 사용하였다. 입력 SNR이 5dB, l0dE, 15dB와 20dB의 각각의 경우에 대하여 SSNR (Segmental SNR)과 잡음 대 마스킹 비 (Noise-to-mask ratio, NMR), 음질 테스트를 수행한 결과, 청감 테스트 (Mean Opinion Score, MOS Test)결과의 향상과 음질의 개선을 확인할 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1399-1404
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• 2000