• The Journal of the Acoustical Society of Korea
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• v.40 no.3
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• pp.247-253
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• 2021

Directional ultrasonic speakers that are used to hear sound only in a specific area have been continuously researched on various improvements in terms of sound quality and cost compared to general speakers. In this paper, we propose a DSP based hybrid-type ultrasonic speaker that can be heard at the same time as a general speaker in order to compensate for the sound in the low-band range, considering that it is difficult to hear the low-band sound below 500 Hz due to the sensor characteristics of the ultrasonic speaker. In the case of the system that is implemented by simply connecting a general speaker and an ultrasonic speaker, there are issues of high cost and difficulties of control as two amplifiers are used to playback ultrasonic and general sound sources. In addition, sound quality deteriorates due to the difference in playback time between ultrasonic and general sound sources. In order to improve issues of cost, control and sound quality, we developed hybrid-type ultrasonic speaker with a DSP based amplifier that can simultaneously playback by synchronizing the general sound source with the regenerated ultrasonic sound source, in addition to implement the existing CODEC functions such as Dynamic Range Control (DRC) and Equalizer (EQ).

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.1
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• pp.141-151
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• 2022

Wireless earphones are products that are consumed together with smart devices (mobile phones, etc), and there is no twisting and convenience compared to general earphones. However, due to the lack of information on the quality of wireless earphones, consumers tend to purchase products based on brand awareness, and manufacturers deliver information to consumers based on different standards for each product due to the lack of standards for measurement methods for quality evaluation. In particular, the playback time of wireless earphones is a factor that can directly affect consumers' purchases, so it is necessary to prepare a standardized test method to properly measure it. This paper introduces the current status of wireless earphones and related standard trends, and proposes a method for measuring the audio playback time of wireless earphones developed through this. In addition, this measurement method will be proposed as an international standard (IEC) after being established as the national standard, the Korean Industrial Standard (KS).

• The Korean Journal of Zoology
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• v.39 no.3
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• pp.282-291
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• 1996

The song of the bush warbler, Cettia diphone, consists of an introdudory whisde portion and a complex ending syllable portion. In bush warbiers, a song with two or fewer notes in the whistle portion is classified as an a song mode, while a song with three or more notes in the whistle portion as a $\beta$ song mode. Although some variations occur in mode seledion by individuals and populations, the proportion of a mode songs to total songs is 55% (range 51.6-58.7%) on average. The a mode has a higher dominant frequency in the whistle portion than does the $\beta$ mode, but the number of syllables m the complex ending syllable portion is fewer. Bush warbler mode sequences are defined as $\alpha$$\alpha$, $\alpha$$\beta$, $\beta$$\alpha$ and $\beta$$\beta$ mode sequences. In order to test the hypothesis that song modes and mode sequences play a role in the defence of territory in Jeju and Wando populations in the south-coastal geographic song variation group, playback experiments were executed. Mode sequences differed between naturally produced songs and songs produced in response to playback for two populations. In particular, for birds in the Wando populations our results indicate that the use of song modes may be affeded by habitat, singing site and type of territory, and further propose that particular mode sequences may play a more important role than song mode in vocal interadions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9B
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• pp.1643-1651
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• 1999

Video-On-Demand (VOD) is expected to provide the user with interactive operations such as VCR functions. In particular, fast scan functions like “Fast Forward” of “Fast Backward” for a certain speedup playback are required. Since they require a significant amount of system resources, schemes to reduce bandwidth requirements for the network or disk are needed. In MPEG standard, Group-of-Pictures (GoP) is a random access unit which can be decoded independently. Since storing and transmitting a video stream based on GoP is efficient, it is practical to support fast scan functions based on GoP. In this paper, we present a dynamic transmission scheduling scheme to support fast scan functions with m-times normal playback rate for a stored video. The proposed scheme writes a transmission schedule whenever user requests a fast scan function. That is, the scheme constructs the data set to be smoothed by skipping GoPs according to a given speedup factor, and then writes the transmission schedule by applying a bandwidth smoothing. Finally, the scheme restarts the transmission of video data to a client according to the new schedule. The proposed scheme results in speeding up the playback rate by utilizing “GoP skipping”, and then reduces the computational overhead by applying a bandwidth smoothing based on GoP.

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.5
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• pp.213-217
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• 2001

Excessive memory buffer requirement in continuous media playback is a serious impediment of wide spread usage of on-line multimedia service. Skewed access frequency of available video files provides an opportunity of re-using the date blocks which has been loaded by one session for later usage. We present novel algorithm which minimizes the buffer requirement in multiple sessions of multimedia playbacks. In continuous media playback originated from the disk, a certain amount of memory buffer is required to synchronize asynchronous disk. Read operation and synchronous playback operation. As aggregate playback bandwodth increases, larger amount of buffer needs to be allocated for this synchronization purpose. The focus of this work is to study the asymptotic behavior of the synchronization buffer requirement and to develop an algorithm coping with this excessive buffer requirement under bandwidth congestioon. We argue that in a large scale continuous media server, it may not be necessary to read the blocks for each session directly from the disk. The beauty of our work lies in the fact that it dynamically adapts to disk utilization of the server and finds the optimal way of servicinh the individual sessions while minimizing the overall buffer space requirement. Optimality of the proposed algorithm is shown by proof. The effectiveness and performance of the proposed scheme is examined via simulation.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.11a
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• pp.250-250
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• 2004

• Journal of the Korean Society for Precision Engineering
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• v.30 no.6
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• pp.615-621
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• 2013

The robot calibration has greatly improved the absolute accuracy of the industrial robot. However, the accuracy of the relative positions of robotic tool-tip at work-points on a work-piece is only slightly corrected by the robot calibration since there has been no practical method to eliminate the elements of the setup position errors at a robotic workplace. A robotic workplace calibration is demonstrated in this paper to minimize the relative position errors between a robot tool-tip and the work-point on a work-piece. The existing teaching and playback method has been developed for the robotic workplace calibration. This paper uses the work-piece fixed in a robotic work-place as measurement equipment instead of a special robot measurement equipment for the robotic workplace calibration. The positive effect of the robotic workplace calibration is supported by the results of computer simulation on an ideal robotic workplace model and an experiment at the actual robotic workplace.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.7
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• pp.489-494
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• 2009

Since multimedia content is often independently encoded into multiple variations having diverse bandwidths, resolutions and compression formats, the same segment might be stored at different temporal positions within the variations. In this paper, we present a durable multimedia bookmark mechanism which provides a convenient way of switching to any variation before or during playback of the multimedia content, without experiencing temporal discontinuity or overlapping a portion of the content. We also present a new multimedia bookmark player with which users can manage a personal collection of bookmarks with an intuitive visual interface.

• 한국HCI학회:학술대회논문집
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• 2008.02a
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• pp.510-516
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• 2008

In ubiquitous environment, there are no limits to utilize networks whenever and wherever you are. That pervasive networks are combined with the information devices and then create various services such as car navigation of LBS(location based service) and DMB(Digital Multimedia Broadcasting). As these kinds of services are getting more various, the complexity is also getting higher and ultimately the convergence will make people feel frustrated. One of the solutions is Context-Awareness[1] technology. User interface with context-awareness filters unnecessary information and prevents users from being blocked due to the massive information. In this paper, we describe the seamless service system based on location-awareness, which is a type of context-awareness. We developed the system based on UPnP AV Framework. This system provides the automatic terminal device selection for the nomadic user. The system establishes new connections for the ongoing streaming playback session with the new AV devices without substantial loss of playback so that the user can enjoy the seamless service. The AV device selection based on the user's location needs no user's intervention or notification so it achieves the improvement of usability and complexity.

• Journal of Internet Computing and Services
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• v.8 no.5
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• pp.59-66
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• 2007

In korea, TIT(Transport Information Technology) based IP-TV services have been provided in Saemaeul trains and some sections of subway trains, But the software systems for the service performed in alternated fashions and suffered from many problems such as suspension, memory leaking and overflow, These problems increased playback loss time and resulted in bad reliabilities, In this paper, a software TIT monitor is designed and implemented for Monitoring module and Reset module in physically poor environments, The designed system formalized monitoring time intervals for effective monitoring, Through the real experiments, playback time is improved in 7.2% comparing to existing system.