• The Journal of the Acoustical Society of Korea
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• v.25 no.6
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• pp.291-297
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• 2006

This paper proposes a new Digital Reverberator that models Analog Helical Coil Spring Reverberator for guitar amplifiers. While the conventional digital reverberators are proposed to provide better sound field mainly based on room acoustics, no algorithm or analysis of digital reverberators those model Helical Coil Spring Reverberator was proposed. Considering the fact that approximately $70{\sim}80$ percent of guitar amplifiers are still with Helical Coil Spring Reverberator, research was performed based not on Room Acoustics but on Helical Coil Spring Reverberator itself as an effector. After performing simulations with proposed algorithm, it was confirmed that the Digital Reverberator by proposed algorithm provides perceptually equivalent response to the conventional Analog Helical Coil Spring Reverberators.

• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.432-440
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• 2009

Recently, the necessity of underwater acoustic communication and demand for transmitting and receiving various data such as voice or high resolution image data are increasing as well. The performance of underwater acoustic communication system is influenced by underwater channel characteristic. Especially, a delay spread caused by reverberation and multi-path induces the ISI (Inter-Symbol-Interference) and reduces the communication performance. In this paper, we study the OFDM (Orthogonal Frequency Division Multiplexing) technique for robust the delay spread in underwater channel. We also use the clipping method to overcome the performance degradation in high PAPR (Peak-to-Average Power Ratio). We confirm the performances of underwater communication system by the underwater channel model simulation model and experiment in small water tank. As a result, the multi-carrier modulation with clipping method presented low BER and the previous single carrier modulation had high BER.

• The Journal of the Acoustical Society of Korea
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• v.29 no.7
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• pp.411-421
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• 2010

A time-reversal mirror (TRM) is useful in diverse areas, such as reverberation ing, target echo enhancement and underwater communication. In underwater communication, the bit error rate has been improved significantly due to the increased signal-to-noise ratio by spatio-temporal focusing. This paper deals with two issues. First, the optimal number of array elements for a given environment was investigated based on the exploitation of spatial diversity. Second, an algorithm was developed to determine the optimal location of the given number of array elements. The formulation is based on a genetic algorithm maximizing the contrast between the foci and area of interest as an objective function. In addition, the developed algorithm was applied to the matched field processing with ocean experimental data for verification. The sea-going data and simulation showed almost 3 dB improvement in the output power at the foci when the array elements were optimally distributed.

• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.461-470
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• 2009

We investigate and analyze the problems encountered in frame-based estimation of TDOA (Time Difference of Arrival) using CPSP function. Spectral leakage occurring in framing of a speech signal by a rectangular window could make estimation of CPSP spectrum inaccurate. Framing with other windows to reduce the spectral leakage distorts the signal due to the asynchronous weighting around the frame specifically both ends of the frame. These problems degrade the performance of the CPSP-based TDOA estimation. In this paper, we propose a method to alleviate those problems by pre-emphasis of the speech signal. It reduces the influence of the spectral leakage by reducing dynamic range of the spectrum of a speech signal with pre-emphasis. To validate the proposed method of pre-emphasis, we carry out TDOA estimation experiments in various noise and reverberation conditions, Experimental results have shown that the framing of pre-emphasized microphone output by a rectangular window achieves higher success rate of TDOA estimation than any other framing methods.

• The Journal of the Acoustical Society of Korea
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• v.33 no.5
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• pp.316-325
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• 2014

The basic unit of school is a classroom and the aural environment of the classrooms is essential factor for education purposes. Therefore, many efforts have been undertaken for enhancing the acoustical performance of the classrooms in many countries. As a result, acoustic criteria including reverberation time and background noise level have been established in US and UK for school classrooms depending on the usage and size of the rooms. However, in Korea, there has been little researches concerning the room acoustical investigations of the classrooms. The present study investigates the current situation of the aural environment of the 15 classrooms in Korea including elementary, middle and high schools. The acoustic criteria measured include RT, $D_{50}$, STI, SNR and background noise level. As the results, it was found that the background noise levels of the schools adjacent to roads exceed the US and UK standard of 35 dB(A). Also, most schools have so low SNR that they may be interfered by noise, which may affect speech transmission. It was also revealed that some schools have longer RT than the US standard of 0.6 s, but they all have high speech intelligibility.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.329-337
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• 2017

In USA and UK, the standards of both reverberation time and background noise level have been established for the appropriate aural environment in classrooms. In order to realize this, guidelines for architectural planning and interior finishing have been also suggested. However, in Korea, there has hardly been any guidelines for satisfying background noise criteria and investigation about sound insulation performance of current walls of classrooms. The present study investigates the structure of outer wall and walls between classrooms of two middle schools in order to analyze the sound insulation performance against both exterior and interior noises. Acoustic parameters including transmission loss, standardized sound level difference, and signal to noise ratio have been measured and analyzed for sound insulation performance of walls and flanking noises. As a result, concerning the walls in between classrooms, it was found that walls of dry construction have greater sound insulation performance rather than the walls of wet construction especially in mid and high frequency bands. Also, It was revealed that thermopane, insulated pair glass, of outer walls, has greater sound insulation performance than the double window consisted of two single pane glass. Regarding flanking noises, the standards were exceeded when all windows, or windows and doors front onto corridor were opened. It denotes that students could be disturbed with the sound transmission by the interior noises.

• The Journal of the Acoustical Society of Korea
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• v.34 no.6
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• pp.411-422
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• 2015

This paper presents an overview of the geological environment investigation and underwater acoustic measurements for the purpose of "Study on the Relationship between the Geological Environment and Acoustic Propagation in Shallow Water", which are jointly carried out by KIOST (Korea Institute of Ocean Science & Technology) and Hanyang University in the western shallow water off the Taean peninsula in the Yellow Sea in April-May 2013. The experimental site was made up of various sediment types and bedforms due to the strong tidal currents and coastal geomorphological characteristics. The geological characteristics of the study area were intensively investigated using multi-beam echo sounder, sub-bottom profiler, sparker system and grab sampler. Acoustic measurements with a wide range of research topics in a frequency range of 20~16,000 Hz: 1) low frequency sound propagation, 2) mid-frequency bottom loss, 3) spatial coherence analysis of ambient noise, and 4) mid- frequency bottom backscattering were performed using low- and mid-frequency sound sources and vertical line array. This paper summarizes the topics that motivated the experiment, methodologies of the acoustic measurements, and acoustic data analysis based on the measured geological characteristics, and describes summary results of the geological, meteorological, and oceanographic conditions found during the experiments.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.5
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• pp.55-65
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• 2016

Detecting an object which is located at seabed is an important issue for various areas. This paper presents an approach to detection of an object that is placed at seabed in the shallow water. A conventional scheme is to employ a side-scan sonar to obtain images of a detection area and to use image processing schemes to recognize an object. Since this approach relies on high frequency signals to get clear images, its detection range becomes shorter and the processing time is getting longer. In this paper, we consider an active sonar system that is repeatedly sending a linear frequency modulated signal of 6~20 kHz in the shallow water of 100m depth. The proposed approach is to model consecutively received reflected signals and to measure their modeling error magnitudes which decide the existence of an object placed on seabed depending on relative magnitude with respect to threshold value. The feature of this approach is to only require an assumption that the seabed consists of an homogeneous sediment, and not to require a prior information on the specific properties of the sediment. We verify the proposed approach in terms of detection probability through computer simulation.

• The Journal of Korean Physical Therapy
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• v.14 no.4
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• pp.172-182
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• 2002

Objectives: We did research in the cause of the Pitchers' injury and their recovery process to make a detailed injury list for the purpose of finding the cause of the Korean professional pitchers' injury and its classification. We drew the conclusion through the results as following. Methods: We posed a question to the 80 pitchers playing in the first team of the eight Korean professional baseball team and analyzed the 62 pieces of question paper except the paper having a mistake. We used SAS/PC statistical package in analyzing the data. Results: In the frequency of the pitchers' shoulder injury in the last three years, the injured of all the players were 61.3$\%$ and the injury free players were 28.7$\%$. The cause of the injury was 45.2$\%$ wrong pitching motion, which was the highest value. For the shape of a pain when injured, the reverberation ache feeling when he is hit in the weight commanded an absolute majority as 19.4$\%$. Those who had muscular pain were 17.7$\%$, which was felt mostly at the pitching motion. The most trouble name of the injured shoulder was bicepstendinitis as 16.1$\%$ while the injury of shoulder joint was the lowest as 1.6$\%$. As the most widely used treatment, 25.8 percent of all the players had taken an electronical thraphy after injury. 14.5 percent of the players who had an injury to the shoulder told that they have an operation and 85 percent of them didn't. As a sort of the operation, a repairing of labrum was 44.4 percent, which is the highest value and the 77.8 percent pitchers are performing a normal pitching through rehabilitation after the operation and 22.2 percent of them are undergoing rehabilitation training. Conclusion: The research have shown that the main cause of the injury, concerning the Korean professional pitchers throwing lots of ball in both matches and practices, is overuse syndrome, bad mechanism, muscle weakness and instability of balance. I think that the role of trainer, physical therapy, and team physician taking charge of the players' injury must learn physical test method by heart exactly to check up the state of the injury definitely at the initial phase. Moreover, when the cause of the injury part after a close examination is discovered, the scientific and good surgery is essential to the rehabilitation success and making a classification of shoulder instability is useful to make a operation plan as well as the players' rehabilitation, treatment.

• (The) Research of the performance art and culture
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• no.35
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• pp.175-202
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• 2017

In this article, I focused on the identity of the Japanese magician, Tenkatsu(天勝), who appeared in Exhibition of Joseon, 1915, and the social gaze and reverberation of them. I would like to see how Tenkatsu group appeared, how it was active, and how it was utilized. Because It was a big stimulus for traditional performing artists. 'Ma-sul' was a new word, taking the place of 'Hwan-sul(幻術)' or 'Hwan-hee'(幻?) for a term of english 'Magic'. In the various articles published during the Japanese colonial period, we can find the performers of the contemporary magic and the Korean artists who tried to make them nationalized. In the mid-1920s, a magician of Korean origin appeared. Kim Mun-phil(김문필), Park Chang-sun(박창순), Kim Wan-shil(김완실) were them. They had experience of studying abroad, such as Russia, and were also helped by religion, the Chondo-kyo. They attracted popularity while touring around the country. Incidents of social problems often arise by linking magic to a form of fraud, though. But the appearance of a Korean magician confirms the existence of a performer who actively engages in new performances.