• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.192-198
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• 2022

As an effective weapon system for anti-submarine warfare, DIrectional Frequency Analysis and Recording (DIFAR) sonobuoy detects underwater targets via beamforming with three channels composed of an omni-direcitonal and two directional channels. However, ambient noise degrades the detection performance of DIFAR sonobouy in specific direction (0°, 90°, 180°, 270°). Thus, an ambient noise redcution technique is proposed for performance improvement of acoustic target detection of DIFAR sonobuoy. The proposed method is based on OTA (Order Truncate Average), which is widely used in sonar signal processing area, for ambient noise estimation and Wiener filtering, which is widely used in speech signal processing area, for noise reduction. For evaluation, we compare mean square errors of target bearing estmation results of conventional and proposed methods and we confirmed that the proposed method is effective under 0 dB signal-to-noise ratio.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2003.11a
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• pp.89-93
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• 2003

The ambient noise in modem society is the factor to give people serious influence. Noise barriers installation is mostly used in the apartment estate to protect countermeasure about the road traffic ambient noise. The purpose of this study is to suggest reference data fur design of traffic noise reduction in apartment estate. It finds out how the traffic noise is measured about a noise barriers and physical characteristics. The 57dB was measured from the noise barriers in a 2m point. An ambient noise's of the part to belong noise attenuation is big at the sound arresting area of the noise barriers as the distance far.

• Journal of Korean Association for Spatial Structures
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• v.17 no.1
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• pp.93-100
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• 2017

With increasing number construction of high-rise building which has about 40 to 60 floors there have been many kinds of problem which related with usage from vibration. To predict response acceleration, it is important to assess correct natural frequency. However, due to the noise of MEMS sensor, it is difficult to measure dynamic characteristic such as natural frequency when measuring ambient vibration using MEMS sensor within cell phone. Therefore, a comparative analysis on vibration measuring applications was performed after measuring ambient vibration of 2 skyscrappers which have height between 133.5~244.3m that are located in Seoul and Observation tower using I-jishin APP with noise reduction function of MEMS sensor in order to verify the effectiveness of low noise type vibration measurement APP.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.260-263
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• 2000

A technique that uses linear prediction to achieve noise reduction in a voice signal which has been mixed with an ambient noise (Signal to Noise (S-N) ratio = about 0dB) is proposed. This noise reduction method which is based on the linear prediction estimates the voice spectrum while ignoring the spectrum of the noise. The performance of the noise reduction method is first examined using the transversal linear predictor filter. However, with this method there is deterioration in the tone quality of the predicted voice due to the low level of the S-N ratio. An additional processing circuit is then proposed so as to adjust the noise reduction circuit with an aim of improving the problem of tone deterioration. Next, we consider a practical application where the effects of round on errors arising from fixed-point computation has to be minimized. This minimization is achieved by using the lattice predictor filter which in comparison to the transversal type, is Down to be less sensitive to the round-off error associated with finite word length operations. Finally, we consider a practical application where noise reduction is necessary. In this noise reduction method, both the voice spectrum and the actual noise spectrum are estimated. Noise reduction is achieved by using the linear predictor filter which includes the control of the predictor filter coefficient’s update.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.1
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• pp.70-74
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• 2008

We are using COS to purpose blocking the excess current and to protect the transformer. But the fuse of COS is melt due to the overload if the excess current flows and it destroy an air severing relations to clear as strong arc happens. Such phenomenon induces an impact ambient noise and it gives the circumstance area resident or pedestrian the fear. Thus, We are the actual circumstances which an ambient noise countermeasure establishment have desired urgently. In this study, we grasp the characteristic of an impact ambient noise which a COS fuse happens the melting and study the method to reduce an impact ambient noise.

• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.454-460
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• 2009

In this paper, we propose a residual echo and noise reduction scheme by using linear predictor for hands-free telephony applications. The proposed scheme whitens residual echo by the linear prediction during the non double-talk. But whitened residual echo signal still has speech characteristics. In this scheme, the whitened residual echo signal is more whitened by using the power of the linear prediction error signal and the linear predicted signal. After whitening process, near-end speech and ambient noise is present during double-talk but white noise will appear during non double-talk situation. By linearly predicting again the combined signal of the near-end speech and the whitened signal, the ambient noise is removed. Through computer simulation, it is shown that the proposed method performs well at the side of AIC (acoustic interference cancellation).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.687-692
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• 2002

In order to verify the effectiveness of adding visooelastic dampers to full-scale steel frame structure on the reduction of their seismic and wind response a experimental work was carried out. First, The test was conducted on the VE dampers subjected to sinusoidal excitations under a variety of ambient temperatures, frequency, and the damper strain. Results from these tests showed that the viscoelastic dampers have high energy dissipation capacity. Second, The vibration tests was conducted of the full-scale steel frame structure with md without added VE dampers at different temperatures. Viscoelastically damped full-scale structure test result on the effect of ambient temperature show that viscoelastic dampers are very effective in reducing excessive vibration of the structure due to sinusoidal excitation over a wide ringe of ambient temperature.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.12
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• pp.1756-1760
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• 2015

This paper focuses on a priori signal to noise ratio (SNR) estimation method for the speech enhancement. There are many researches for speech enhancement with several ambient noise cancellation methods. The method based on spectral subtraction (SS) which is widely used in noise reduction has a trade-off between the performance and the distortion of the signals. So the need of adaptive method like an estimated a priori SNR being able to making a high performance and low distortion is increasing. The decision directed (DD) approach is used to determine a priori SNR in noisy speech signals. A priori SNR is estimated by using only the magnitude components and consequently follows a posteriori SNR with one frame delay. We propose a modified a priori SNR estimator and the weighted rational transfer function for speech enhancement with wind noises. The experimental result shows the performance of our proposed estimator is better Perceptual Evaluation of Speech Quality scores (PESQ, ITU-T P.862) compare to the conventional DD approach-based systems and different noise reduction methods.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.242-242
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• 2013

Recently, importance of working environment is increased in commercial vessel and offshore structure. Marine facility design and ambient environment condition are influenced to enhancing human performance and reducing human errors. Consequently, the quality of accommodation where offshore facility crews sleep, eat and relax will influence their job performance and overall sense of comport and well-being. Therefore, adequate acoustic isolation between adjacent spaces is normally required to achieve satisfactory internal noise levels, acoustic privacy and speech intelligibility. In this study, the reverberation time is investigated in the public areas where there are not provided the information of material's noise reduction coefficient (NRC). The experiment of reverberation time is rarely performed for the various type public areas in a marine structure. Therefore, the reverberation time in a vessel is investigate in order to evaluate the room's noise reduction coefficient (NRC) in a public area.