• Journal of rehabilitation welfare engineering & assistive technology
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• v.1 no.1
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• pp.21-28
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• 2007

In most of hearing aids, amplification algorithms are used to compensate hearing loss, noise and feedback reduction algorithms are used and to increase the perception of speeches contrast enhancement algorithms are used. However, acoustic masking effect is occurred between formants if contrast is enhanced excessively. To confirm the masking effect in speeches, the experiment are composed of 6 tests; test pure tone test, speech reception test, word recognition test, pure tone masking test, formant pure tone masking test and speech masking test, and for objective evaluation, LLR is introduced. As a result of normal hearing subjects and hearing impaired subjects, more making is occurred in hearing impaired subjects than normal hearing subjects when using pure tone, and in the speech masking test, speech reception is also lower in hearing impaired subjects than in normal hearing subjects. This means that acoustic masking effect rather than distortion influences speech perception. So it is required to check the characteristics of masking effect before wearing a hearing aid and to apply this characteristics to fitting curve.

• Journal of the Korean Institute of Intelligent Systems
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• v.13 no.6
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• pp.698-703
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• 2003

This paper presents analog secure communication system about safe speech transmission using chaotic signals. We applied various conditions that happen in actuality communication environment modifying chaotic synchronization and chaotic communication schemes and analyzed restoration performance of speech signal to computer simulation. In transmitter, we made the chaotic masking signal which is added voice signal to chaotic signal using PC(Pecora ＆ Carroll) and SFB(self-feedback) control techniques and transmitted encryption signal to noisy communication channel And in order to calculate the degree of restoration performance, we proposed the definition of analog average power of recovered error signals in receiver chaotic system. The simulation results show that feedback control techniques can certify that restoration performance is superior to quantitative data than PC method about masking degree, susceptibility of parameters and channel noise. We experimentally computed the table of relation of parameter fluxion to restoration error rate which is applied the encryption key values to the chaotic secure communication.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.5
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• pp.13-20
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• 2008

Although digital hearing aid algorithms have been developed to compensate hearing loss and to help hearing impaired people to communicate with others, digital hearing aid user still complain about difficulty of hearing the speech. The reason could be the quality of speech through digital hearing aid is insufficient to understand the speech caused by feedback, residual noise and etc. And another thing is masking effect among formants that makes sound quality low. In this study, we measured the masking characteristics of normal listeners and hearing impaired listeners having presbyacusis to confirm masking effect in speech itself. The experiment is composed of 5 tests; pure tone test, speech reception threshold (SRT) test, word recognition score (WRS) test, puretone masking test and speech masking test. In speech masking test, there are 25 speeches in each speech set. And log likelihood ratio (LLR) is introduced to evaluate the distortion of each speech objectively. As a result, the speech perception became lower by increasing the quantity of formant enhancement. And each enhanced speech in a speech set has statistically similar LLR, however speech perception is not. It means that acoustic masking effect rather than distortion influences speech perception. In actuality, according to the result of frequency analysis of the speech that people can not answer correctly, level difference between first formant and second formant is about 35dB, and it is similar to result of pure tone masking test(normal hearing subject:36.36dB, hearing impaired subject:32.86dB). Characteristics of masking effect is not similar between normal listeners and hearing impaired listeners. So it is required to check the characteristics of masking effect before wearing a hearing aid and to apply this characteristics to fitting.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.46.1-46.1
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• 2014

In understanding "cooling flow" problem and the galaxy-SMBH co-evolution, AGN feedback is considered as one of the most important phenomena. Among various AGN feedback phenomena, X-ray cavities are particularly useful for studying AGN feedback over 10 kpc scales, as the origin of X-ray cavities is believed to be related to radio jet from AGN. For a comprehensive study of X-ray cavities, we collect all available diffuse X-ray data of galaxies in various galaxy environments, ranging from field galaxies to galaxy clusters, using the Chandra X-ray data archive. As a result we build up a sample of 87 targets showing enough X-ray photons to perform the analysis. Using modeling and unsharp masking techniques, we detected X-ray cavities and measured their physical properties (i.e., cavity size) for the 49 targets. Here, we present X-ray cavity properties and discuss environmental effects.

• Journal of Broadcast Engineering
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• v.1 no.1
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• pp.62-66
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• 1996

In this paper, we consider a signal masking structure based on the Lorenz system, which uses a feedback path of the information signal in the transmitter system. The scheme recovers the information signal exactly at the receiver, and can be used with increased amplitude information signal. The scrambling property of the scheme is also investigated by computer simulations, from which the performance is show to be better than that of the conventional method.

• The Journal of the Korea Contents Association
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• v.17 no.3
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• pp.359-369
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• 2017

The purpose of this study was to examine whether the effect of feedback would mask the performance differences that would result from different incentive pay distribution. Five critical service behaviors were identified and measured daily at a gas station located in Seoul. Participants were 5 employees working at the gas station. Independent variables were the types of incentive distribution and feedback. After baseline (A), equally-distributed group incentive condition (B) was introduced, and individual incentive condition (C) was introduced in the next phase. Then, after the withdrawal condition (A'), equally-distributed group incentive with feedback condition (B') was introduced and finally, the individual incentive with feedback condition (C') was introduced. The results suggested that all employees showed higher work performance under individual incentive than equally-distributed group incentive system when feedback were not delivered. However, there was no difference in work performance between two incentive conditions in the phases in which feedback were delivered. These findings suggest that feedback can reduce performance differences between equally-distributed group incentives and individual incentives.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.34.2-34.2
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• 2016

X-ray cavities are typically detected as surface brightness depression in X-ray diffuse emission from hot gas in high resolution X-ray images (i.e., Chandra and XMM-Newton). Showing the coincidence of location with radio jets, X-ray cavities imply that the radio jets interact with interstellar/intergalactic medium. It is important to understand them since they can be a clue of understanding AGN feedback to their host galaxies. To understand the physics of the AGN feedback, X-ray cavity has been actively studied while there are only a few statistical studies on X-ray cavity based on small or incomplete samples. Hence, a systematic study with a large sample is needed. With the condition of sufficient X-ray photons to detect surface brightness depression, we constructed a large sample of 133 galaxy clusters, galaxy groups, and individual galaxies to investigate X-ray cavities. We detected 201 cavities from 94 objects using two detection methods (i.e., beta-modeling and unsharp masking method), and confirmed the cavity size-distance relation over a large dynamical range. The size-distance relation does not vary for different environments (i.e., galaxy cluster, groups, and individual galaxies), suggesting that there is little environmental effect on the formation of X-ray cavity.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2002.12a
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• pp.353-356
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• 2002

본 논문은 카오스 신호를 이용하여 안전한 음성신호의 전송을 위한 아날로그 비화통신 시스템의 성능분석에 관한 연구이다. 기존의 카오스 동기화 및 카오스 변조통신 알고리즘을 개선하여 실제 통신환경에서 발생하는 다양한 조건들을 적용하여 음성신호의 복원능력을 모의실험으로 분석하였다. 일반적인 PC 제어기법과 제안한 피드백 마스킹 기법을 사용하여 송신단에서 음성신호를 카오스 신호로 마스킹하여 변조하고, 통신채널에 잡음신호를 추가하여 전송하였다. 수신단에서는 카오스 응답시스템을 이용하여 음성신호를 복조하고, 복원성능을 계산하기 위하여 아날로그 복원 에러신호의 평균전력을 제안하여 계산하였다. 실험결과 마스킹 정도, 파라미터들의 민감성, 채널잡음 등에 대하여 PC 제어기법보다 피드백 제어기법의 복원성능이 우수함을 확인할 수 있었다. 또한 로렌쯔 카오스 시스템을 비화통신시스템에 사용할 경우 파라미터들의 조합으로 암호키를 구성해야 하므로 키값들의 선정에 기준이 되는 파라미터 변화율에 대응하는 복원에러율의 관계를 실험 값으로 구하였다.