• The Journal of the Acoustical Society of Korea
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• v.38 no.1
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• pp.30-38
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• 2019

In recent years, researches on various communication methods have been conducted, particularly on OFDM (Orthogonal Frequency Division Multiplexing) and CDMA (Code Division Multiple Access) methods, as the use of underwater communication increases. While OFDM is, in general, advantageous in that it is resistant to Doppler in the water and it enables a high-speed communication, CDMA is resistant to frequency selective fading in the water and it can reduce energy consumption. Therefore, in this paper, we performed experiments in the shallow water in Western Sea of Korea to analyze the performance of OFDM and CDMA communication systems in the underwater channel environment. The maximum delay spread and Doppler spread were drawn by using the data obtained from the real sea area in order to analyze the underwater channel environment characteristics of the shallow water in Western Sea of Korea. The communication performances of OFDM and CDMA are shown as coded BER (Bit Error Rate) according to the variation of the maximum delay spread and the Doppler spread, respectively. The result of the analysis show that the OFDM method has more resistant performances to the underwater channel environment changes than the CDMA method.

• Journal of Science Education
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• v.45 no.1
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• pp.69-89
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• 2021

The purpose of this study is to examine personal characteristics of two elementary students who developed individual interest in science. 201 students of two elementary schools in Seoul participated in questionnaire survey engaged in to investigate students' interest in science, engagements and preference in science-related-activities three times a year. This case study was conducted with seven students who showed typical types of interest in science. Students wrote a photo-journal for 12 weeks. They were interviewed every other week by a researcher. We analyzed two students who developed individual interest. It turns out that RF participated in doing experiments at home, and disassembling and assembling things. Participation of activities was a process of solving curiosity. When he was unable to solve problems, he searches the internet or books. Sometimes he would ask for help from his teacher. JW engaged in activities: drawing, doing experiments at home, and going to informal education center. She communicated with others by using online-offline media. Curious questions were solved by herself. The two students have a tendency to solve problems by themselves. Also, positive science-related activities were going on at home and in school. This study not only give insights and understanding of students who developed individual interest in science but also provide implication for educators to examine personal characteristics of students.

• Industry Promotion Research
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• v.6 no.1
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• pp.55-62
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• 2021

This study regards the need for jobs to overcome the poverty of the elderly in an aged society, and as well as researches ways to participate in active economic activities in old age. The results of the study are as follows. First, the legal system needs to be improved. In addition to institutional support for the expansion of jobs for the elderly, improvement of awareness of the elderly and reinforcement of infrastructure such as a delivery system are required, and a legal basis for this is needed. To this end, occupations targeting the elderly must be selected first, and legal procedures must be prepared by the government. Second, there must be social consideration and support for the elderly. Extension of the retirement age plays an important role in enhancing employment for the elderly. Along with the improvement of the legal system, social consideration is required. Therefore, since the elderly policy without social consensus is bound to fail, various support methods that can lead to social support must be devised. Third, the elderly must have a sense of poverty and willingness to rehabilitate themselves. Elderly people should not only ask for their children and social support. The elderly must be able to find a way to become the economic agent themselves. To do this, a basic awareness of the elderly poverty consciousness is needed, and a change of awareness to escape the poverty of the elderly is necessary. Therefore, the elderly need to be self-reliant, and they must choose jobs according to their own abilities. In conclusion, the elderly job program is a part of income increase that solves the poverty of the elderly in the aged society, and the elderly are required to actively participate in economic activities.

• The Journal of the Acoustical Society of Korea
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• v.40 no.1
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• pp.18-30
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• 2021

The ultimate goal of the present study is to establish the acoustical performance standards of classroom for the elderly who are incomplete hearing people. As a pilot survey, the present study was conducted to investigate the listening environment and the actual condition of speech perception performance of education facilities for elderly, Acoustic performances of two education facilities for elderly in Cheongju were measured and questionnaire survey was done to elderly people. Also, speech intelligibility tests were undertaken by Consonant Vowel Consonant (CVC) and Phonetically Balanced Words (PBW) methods. The questionnaire survey showed that the elderly were satisfied with the listening environment of the educational facilities in general. Also, it was found that acoustical performances satisfy with the acoustic criteria of general classrooms in Korea. However, the results of the speech intelligibility test showed that the scores of elderly were significantly lower than twenties with normal hearing. It was also revealed that the scores are reduced as the age increases. Thus, it was concluded that the acoustical performance standards of educational facilities for the normal hearing were not suitable for educational facilities for the elderly.

• The Journal of the Acoustical Society of Korea
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• v.40 no.1
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• pp.55-63
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• 2021

In this study, a numerical methodology is proposed for evaluating valve flow noise in a pipe conveying high pressure gas, and the effects of perforated plates on reduction of such valve flow noise are quantitatively analyzed. First, high-accurate unsteady compressible Large Eddy Simulation techniques are utilized to predict flow and flow noise by a valve in a high-pressure pipe. The validity of the numerical result is confirmed by comparing the predicted wall pressure spectrum with the measured one. Next, the acoustic power of downstream-propagating acoustic waves due to the valve flow is analyzed using an acoustic power formula for acoustic waves propagating on mean flow in a pipe. Based on the analysis results, perforated plates are designed and installed downstream of the valve to suppress the valve flow noise and the acoustic power of downstream-going acoustic waves is predicted by using the same numerical procedure. The reduction by 9.5 dB is confirmed by comparing the predicted result with that of the existing system. Based on these results, the current numerical methodology is expected to be used to reduce valve flow noise in an existing system as well as in a design stage.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.422-428
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• 2021

This study surveyed residents and public officials for the projects to make smart-city plans of Geumsan-gun. First, domestic and foreign cases related to smart city projects were reviewed. The local status of Geumsan-gun was investigated regarding various aspects of the natural, social, urban environment, and smart-city facilities. The survey results were as follows. Overall, more than half of the survey respondents said they were satisfied with their housing quality. Several problems in their areas, such as inefficient welfare system, shortage of parking space, and industrial infrastructure, were reported. On the other hand, tourism and leisure facilities, health care support systems, industries to boost the economy, and the job market were also important issues. The problem was that the regional problems mentioned above were not in line with their preferences for smart-city services. The implications of the survey results could be summed up as follows. The groupware surveys of Geumsan-gun should be used as survey tools, whereas IT survey tools (Google, Survey Monkey, etc.) should be used for locals. In particular, a survey targeting residents should ask plain and compact questions taking advantage of local gatherings. It is also important to have a pilot-survey with relevant public officials and select related projects and regional issues. The survey of local residents and public officials is a prerequisite for promoting smart city projects. The smart city project shall reflect the needs of residents while solving community problems by considering the survey results and local conditions.

• The Journal of the Acoustical Society of Korea
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• v.41 no.4
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• pp.435-445
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• 2022

In this study, the reverberation of a bistatic sonar operated in southeastern coast in the East Sea in July 2020 was analyzed. The reverberation sensor data were collected through an LFM sound source towed by a research vessel and a horizontal line array receiver 1 km to 5 km away from it. The reverberation sensor data was analyzed by various methods including geo-plot after signal processing. Through this, it was confirmed that the angle reflected from the sound source through the scatterer to the receiver has a dominant influence on the distribution of the reverberation sound, and the probability distribution characteristics of bistatic sonar reverberation varies for each beam. In addition, parametric factors of K distribution and Rayleigh distribution were estimated from the sample through moment method estimation. Using the Kolmogorov-Smirnov test at the confidence level of 0.05, the distribution probability of the data was analyzed. As a result, it could be observed that the reverberation follows a Rayleigh probability distribution, and it could be estimated that this was the effect of a low reverberation to noise ratio.

• The Journal of the Acoustical Society of Korea
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• v.41 no.1
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• pp.108-113
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• 2022

Speech recognition in noise situation is an important skill for effective communication. Hearing In Noise Test (HINT) has been suggested as a clinical tool to evaluate these aspects. However, this tool has not been used widely in domestic clinics. In this study, psychophysical aspects of HINT and burdens in clinical application were analyzed to improve the applicability of the tool. The difficulty in understanding speech in the elderly population is due to hearing loss based on aging of peripheral and central auditory pathways. As typical clinical cases, HINT scores for young and elderly listeners (20s vs 70s) were compared. Four conditions of HINT test were Quiet (Q), Noise Front (NF), Noise Right (NR), and Noise Left (NL). Quantitative scores showed that the elderly listener required more Signal to Noris Ratio (SNR) values than the younger counterpart in noisy situations. Although both showed Binaural Masking Level Difference (BMLD) effect, the strength was smaller in the elder. However, the age-matched normalized data were not established in detail for clinical application. Confirmed usefulness of HINT and the related improvement in clinical measuring procedure were suggested.

• The Journal of the Acoustical Society of Korea
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• v.41 no.1
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• pp.38-44
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• 2022

Speech enhancement is performed to improve intelligibility and quality of the noise-corrupted speech. In this paper, speech enhancement performance was compared using different loss functions in time and frequency domains. This study proposes a combination of loss functions to utilize advantage of each domain by considering both the details of spectrum and the speech waveform. In our study, Scale Invariant-Source to Noise Ratio (SI-SNR) is used for the time domain loss function, and Mean Squared Error (MSE) is used for the frequency domain, which is calculated over the complex-valued spectrum and magnitude spectrum. The phase loss is obtained using the sin function. Speech enhancement result is evaluated using Source-to-Distortion Ratio (SDR), Perceptual Evaluation of Speech Quality (PESQ), and Short-Time Objective Intelligibility (STOI). In order to confirm the result of speech enhancement, resulting spectrograms are also compared. The experimental results over the TIMIT database show the highest performance when using combination of SI-SNR and magnitude loss functions.

• The Journal of the Acoustical Society of Korea
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• v.41 no.1
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• pp.76-86
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• 2022

Personal hearing devices, such as hearing aids, may be fine-tuned by allowing the users to conduct self-adjustment. Two self-adjustment procedures were developed to collect the listener preferred gains in six octave-frequency bands from 0.25 kHz to 8 kHz. These procedures were designed to allow rapid exploration of a multi-dimensional parameter space using a simple, one-dimensional user control interface (i.e., a programmable knob). The two procedures differ in whether the user interface controls the gains in all frequency bands simultaneously (Procedure A) or only the gain in one frequency band (Procedure B) on a given trial. Monte-Carlo simulations suggested that for both procedures the gain preference identified by simulated listeners rapidly converged to the ground-truth preferred gain profile over the first 20 trials. Initial behavioral evaluations of the self-adjustment procedures, in terms of test-retest reliability, were conducted using 20 young, normal-hearing listeners. Each estimate of the preferred gain profile took less than 20 minutes. The deviation between two separate estimates of the preferred gain profile, conducted at least a week apart, was about 10 dB ~ 15 dB.