• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.559-567
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• 2020

This paper proposes a noise cancelling algorithm to remove own-ship noise for a towed array sonar. Extra beamforming is performed using partial channels of the acoustic array to get a reference beam signal robust to the noise bearing. Frequency domain Adaptive Noise Cancelling (ANC) is applied based on Normalized Least Mean Square (NLMS) algorithm using the reference beam. The bearing of own-ship noise is estimated from the coherence between the reference beam and input beam signals. Own-ship noise level is calculated using a beampattern of the noise with estimated steering angle, which prevents loss of a target signal by determining whether to update a filter so that removed signal level does not exceed the estimated noise level. Simulation results show the proposed algorithm maintains its performance when the own-ship gets out off its bearing 40 % more than the conventional algorithm's limit and detects the target even when the frequency of the target signal is same with the frequency of the own-ship signal.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.232-232
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• 2020

하천기본계획 수립이나 생태하천 조성사업 등 다양한 하천사업에서 하천측량은 대상 하천의 지형 현황과 과거 사업이후의 변화량을 확인할 수 있는 중요한 요소이다. 국내 측량 기준인 공공측량작업규정(국토지리정보원)에서 하천 측량은 육지부에서는 횡단측량을 수부에서는 수심측량을 실시하고 수심측량은 음향측심기 사용을 원칙으로 한다. 국내 대부분의 수심측량은 단빔 음향측심기를 사용하고 있는 실정이며 일부 수심 확보 구간 또는 연구목적으로 멀티빔 음향측심기를 적용한 사례가 일부 보고된 바가 있다. 최근 수심측정이 가능한 항공수심측량(Airbone LiDAR Bathymetry) 장비 중 핵심계측기기인 Green LiDAR 센서 국산화 및 경량화에 관한 연구가 진행중이다. 이에 본 연구는 국내 하천 여건에서 개발 센서가 어느 정도의 활용성을 확보할 수 있는지를 검토하였다. 우선 환경부가 운영중인 수질자동측정망 71개 지점의 정기측정성과 중 탁도에 관한 일자료를 확보가 가능한 45개 지점을 대상으로 G-LiDAR 센서의 SD(Secchi Depth)를 기준으로 가용계측일을 산정해 보았다. 분석기간은 '12. 7.부터 '19.12.까지이며 분석기간중 SD 1.5m(1.94 NTU 추정) 기준을 만족하는 기간은 한강 2.07년, 낙동강 0.64년, 금강 2.21년, 영산강 2.71년으로 나타났다. 또한 지점별 가용기간 분석결과 분석기간인 7.33년 동안 탁도 기준이하인 운영 가능 기간은 연중 평균 80여일(2.74개월)로 나타나 제한적이나마 활용이 가능할 것으로 확인되었다. 향후 현장조사를 통해 공공측량 성과와 대상수계의 탁도 실측자료와의 연계분석을 통해 정확한 활용성 검토를 수행할 예정이다. 향후 적용 센서의 개발 성능목표를 달성한다면 하천내의 다양한 분야에서 활용이 가능할 것으로 기대된다.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.176-183
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• 2014

Acoustic emission testing (AET) of cylinders is advantageous in that it can be directly conducted on cylinders installed in a car, without needing to dissemble them on a real-time basis. Therefore, users prefer AET over other nondestructive testing methods. Owing to these advantages of AET, it has been approved by the Department of Transportation of the U.S. as a safety evaluation method for pressure containers or as an alternative to the hydroproof testing method. This paper presents a study of the quantitative evaluation criteria for a container having ultrasonic testing defects and also for Type 1 and Type 2 gas cylinders, which are defective seamless pressure containers provided by NK, a manufacturer of pressure containers. For the Type 1 cylinder, the process from crack growth to leak was observed in a repetitive fatigue test using a 113 L container according to ASTM E 1419-02. Further, for the Type 2 cylinder, integrity was evaluated using a 119 L sound container and a container damaged by hydraulic pressure, by the slow-fill method according to ASTM E 2191-02. Based on the AET results of the Type 1 and Type 2 cylinders, quantitative evaluation criteria were established for a defective and non-defective container.

• The Journal of the Acoustical Society of Korea
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• v.19 no.1
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• pp.11-15
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• 2000

Speaker adaptive continuous speech recognition for the RM speech corpus is described in this paper. Learning of hidden markov models for the reference speaker is performed for the training data of RM corpus. For the evaluation, evaluation data of RM corpus are used. Parts of another training data of RM corpus are used for the speaker adaptation. After dynamic time warping of another speaker's data for the reference data is accomplished, error back propagation neural network is used to transform the spectrum between speakers to be recognized and reference speaker. Experimental results to get the best adaptation by tuning the neural network are described. The recognition ratio after adaptation is substantially increased 2.1 times for the word recognition and 4.7 times for the word accuracy for the best.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.10a
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• pp.231-235
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• 2003

실시간 동적 GPS 측위를 이용한 해저수심측량은 GPS 수신기가 이동중인 상태에서 신호단절 없이 연속적인 수심측정이 가능하며 등수심도와 등고선 제작에 정확한 위치를 결정할 수 있고, 음향측심기는 발사파와 수신파의 도달시간을 측정하여 수심을 관측할 수 있기 때문에 실시간으로 정확한 3차원 측량이 가능하다. 본 논문에서는 해안지역에 대한 지형 분석을 하기 위하여 기준점에 대한 정지관측을 실시하여 좌표변환계수를 산출하고, 이로부터 실시간 동적 GPS 측량과 음향측심기를 이용하여 해운대 해수욕장과 해안을 관측하였다. 1:1,200 축척의 수치지도에서 추출한 수치표고모델에서의 체적은 97953.9 ㎥이며, 실시간 동적 GPS와 음향측심기를 이용하여 추출한 수치표고모델에서의 체적은 95994.9 ㎥로 나타났다. 이는 수치지도에서의 체적과 측량결과의 체적이 단지 2.0%정도로 나타나 실시간 동적 GPS와 음향측심기의 결합에 의한 해저수심측량이 매우 성공적임을 알 수 있었다.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.249-252
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• 2002

본 논문에서는 음향반향제거기에서 상관계수를 이용하여 동시통화 구간을 검출하는 방법에서 검출 오류로 인해 발생되는 문제점에 대해서 다룬다. 상관계수(correlation coefficient)를 이용한 DT 검출 방법에서 동시통화 구간과 반향경로의 변화를 명확하게 구분 짓는 문턱값 설정이 어렵기 때문에 때때로 검출 오류가 발생한다. 즉, 동시통화 중간에 반향경로가 변함으로써 동시통화 구간의 끝점 검출에 실패하거나 반항경로 변화를 DT로 잘못 인식하는 경우가 발생하는데, 이럴 경우 더 이상 적응필터의 계수를 갱신을 할 수 없는 상태에 빠지기도 한다. 본 논문에서는 반향제거기에 보조필터를 사용하여 이러한 문제점을 해결하고자 한다. 이는 보조필터가 기준입력신호(reference signal)를 이용하여 변화된 반향신호 성분은 추정할 수 있지만 근단화자 신호는 추정할 수 없다는 점을 이용한다 실험을 통해 제안한 알고리즘이 검출 오류로 인해 발생되는 문제를 효율적으로 해결할 수 있음을 확인하였다.

• The Journal of the Acoustical Society of Korea
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• v.41 no.3
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• pp.302-311
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• 2022

Sound barrier walls are one of the most effective alternatives for reducing environmental noise on roads and railways in the city center. The insertion loss of the sound barrier against road traffic noise is the sum of the sound transmission loss, sound absorption loss, and sound energy reduction due to the diffraction attenuation of the sound barrier. The sound transmission loss of the sound barrier is one of the important factors that determine the insertion loss of the sound barrier and is a basic indicator that determines the performance of the sound barrier. Nevertheless, there is not a separate standard in Korea for measuring the acoustic transmission loss of sound barrier panels. There are only a few conditions in KS F 4770 series that stipulates on the general material of sound barrier panels. This thesis examines the necessity of the acoustic transmission loss measurement and evaluation standards of sound barrier walls, and seeks a measurement method in a free sound field (anechoic chamber) sound receiving room considering the characteristics of sound barrier walls installed in external spaces, unlike indoor building materials. In addition, a single number evaluation method using a reference spectrum was proposed so that the sound insulation effect according to various installation places such as roadside or railroad side can be easily displayed.

• Phonetics and Speech Sciences
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• v.14 no.2
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• pp.55-65
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• 2022

This study aimed to compare acoustic measurements by the high, middle, and low laryngeal heights of male musical theater students. Furthermore, the correlation between the relative height of the larynx and the acoustic measurements was examined, along with the predictability of the relative height (vertical position) of the larynx from acoustic measurements. The participants included five male students majoring in musical theater singing, and acoustic analysis was performed by having them produce the /a/ vowel 10 times each at the laryngeal positions of high, middle, and low. The relative vertical positions of the laryngeal prominence in each position were measured based on the resting position. Results indicated that the relative position of the larynx varied significantly according to laryngeal height, such that as the larynx descended, the first three formant frequencies decreased while the spectral energy at the same frequencies increased. Formant frequencies showed a weak to moderate positive correlation with the relative height of the larynx, while the spectral energy showed a moderate negative correlation. The relative height of the larynx was predicted by eight acoustic measures (adjusted R² = .829). In conclusion, the predictability of the relative height of the larynx was partially confirmed in a non-invasive manner.

• The Journal of the Acoustical Society of Korea
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• v.39 no.5
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• pp.483-489
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• 2020

This paper proposes acoustic model training using self-attention for low-resource speech recognition. In low-resource speech recognition, it is difficult for acoustic model to distinguish certain phones. For example, plosive /d/ and /t/, plosive /g/ and /k/ and affricate /z/ and /ch/. In acoustic model training, the self-attention generates attention weights from the deep neural network model. In this study, these weights handle the similar pronunciation error for low-resource speech recognition. When the proposed method was applied to Time Delay Neural Network-Output gate Projected Gated Recurrent Unit (TNDD-OPGRU)-based acoustic model, the proposed model showed a 5.98 % word error rate. It shows absolute improvement of 0.74 % compared with TDNN-OPGRU model.

• The Journal of the Acoustical Society of Korea
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• v.38 no.3
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• pp.275-282
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• 2019

In airport terminal, aural information is transmitted during 24 hours a day including announcement, background music and emergency control. So, clear sound is mostly necessary to transmitted to the passengers in airports. IIA (Incheon International Airport) is one of the largest airports accommodating 45 million people a year which have been built since 2001. There are currently three passenger terminals including Terminal 1 & 2, and boarding concourse. The $2^{nd}$ passenger terminal is under construction to expand the spaces which will be finished in 2020. The present work aims to explain the design principles of both architectural acoustics and electo-acoustics which have been applied to all the terminal buildings in IIA including ticketing counter, great hall, departure concourse and transportation center. Also, the acoustical performances of those spaces were examined. As a result, acoustic standards for airport were suggested. Architectural concepts for designing ceiling spaces and sound absorption treatments were suggested. Also, electro-acoustic design principles were commented.