• The Journal of the Acoustical Society of Korea
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• v.28 no.2
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• pp.85-95
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• 2009

In the binaural synthesis environments, wide varieties of the head-related transfer functions (HRTFs) that have measured with a various direction would be desirable to obtain the accurate and various spatial sound images. To reduce the size' of HRTFs, interpolation has been often employed, where the HRTF for any direction is obtained by a limited number of the representative HRTFs. In this paper, we study on the distortion measures for interpolation, which has an important role in interpolation. With lhe various objective distortion metrics, the differences between the interpolated and the measured HRTFs were computed. These were then compared and analyzed with the results from the listening tests. From the results, the objective distortion measures were selected, that reflected the perceptual differences in spatial sound image. This measure was employed in a practical interpolation technique. We applied the proposed method to four kinds of an HRTF set, measured from three human heads and one mannequin. As a result, the Mel-frequency cepstral distortion was shown to be a good predictor for the differences in spatial sound location, when three HRTF measured from human, and the time-domain signal to distortion ratio revealed good prediction results for the entire four HRTF sets.

• The Journal of the Acoustical Society of Korea
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• v.28 no.6
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• pp.557-565
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• 2009

To perceive the direction and the distance of a sound, we always use a couple of information. Head Related Transfer Function (HRTF) contains the information that sound arrives from a sound source to the ears of the listener, like differences of level, phase and frequency spectrum. For a reproduction system using 2 channels, we apply HRTF to many algorithms which make 3d sound. But it causes a problem to localize a sound source around a certain places which is called the cone-of-confusion. In this paper, we proposed the new algorithm to reduce the confusion of sound image localization. The difference of frequency spectrum and psychoacoustics theory are used to boost the spectral cue among each directions. To confirm the performance of the algorithm, informal listening tests are carried out. As a result, we can make the improved 3d sound in 2 channel system based on a headphone. Also sound quality of improved 3d sound is much better than conventional methods.

• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.409-415
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• 2009

The head-related transfer function (HRTF), which has an important role in virtual sound localization has different characteristics across the subjects. Measuring HRTF is very time-consuming and requires a set of specific apparatus. Accordingly, HRTF customization is often employed. In this paper, we propose a method to search an adequate HRTF from a set of the HRTFs. To achieve rapid and reliable customization of HRTF, all HRTFs in the database are partitioned, where a binary search tree was employed. The distortion measurement adopted in HRTF partitioning was determined in a heuristic way, which predicts the differences in perceived sound location well. The DC-Davis CIPIC HRTF database set was used to evaluate the effectiveness of the proposed method. In the listening test, where 10 subjects were participated, the stimuli filtered by the HRTF obtained by the proposed method were closer to those by the personalized HRTF in terms of sound localization. Moreover, performance of the proposed method was shown to be superior to the previous customization method, where the HRFT is selected by using anthropometric data.

• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.54-59
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• 2014

Identification of RTF (Relative Transfer Function) between sensors is essential to multichannel speech enhancement system. In this paper, we present an approach for estimating the relative transfer function of speech signal. This method adapts a CASA (Computational Auditory Scene Analysis) technique to the conventional OM-LSA (Optimally-Modified Log-Spectral Amplitude) based approach. Evaluation of the proposed approach is performed under simulated stationary and nonstationary WGN (White Gaussian Noise). Experimental results confirm advantages of the proposed approach.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.29.1-29.1
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• 2009

이 연구는 별 관측을 통해 점 퍼짐 함수(PSF)를 측정하고 나이퀴스트 주파수에서 변조 전달 함수(MTF)을 계산하여 주파수 영역에서 저궤도 광학 위성의 영상품질 평가방법을 도출하였다. 가상 별 영상을 생성하고 IRAF로 2차원의 점 퍼짐 함수를 얻었고 MATLAB으로 점 퍼짐 함수를 2차원 푸리에 변환하여 변조 전달함수를 계산하였다. 공간 영역에서는 점 퍼짐 함수의 모양을 통해서도 영상품질을 검증할 수 있다. Along/Across-Track의 모양이 일치하고 중심에서 좌우대칭이며 델타함수에 가까울수록 좋은 품질의 영상을 의미한다. Along/Across-Track의 점 퍼짐 함수 모양차이는 Line Rate나 Time Delay and Integration(TDI)의 오차에서 기인한다. 별을 점광원으로 본다면 점 퍼짐 함수를 정의하기 쉽고 Along/Across 방향을 동시에 측정 가능하다는 장점이 있다. 궤도상에서 별을 관측하는 것은 지상을 관측하는 것보다 대기 환경의 효과가 크지 않기 때문에 영상 품질 평가에 유리하다. Yaw Steering이나 Nadir Pointing과 같은 자세제어의 효과를 배제할 수 있으므로 자세제어의 효과가 상당 부분 제거된 영상품질을 분석할 수 있다. 지상관측시간이나 배터리 충전시간이 아닌 지구 본영에서 별을 관측하므로 임무에 방해받지 않는다. 지상관측과 같은 효과를 내고 TDI를 사용하는 환경을 구현하기위해 Line Rate를 고려한 자세 기동 방법에 대해 연구하였다. 큰 각도의 자세 기동이 예상되어 쿼터니안을 이용하여 Inertial Pointing하도록 자세 제어하였고, 자세 Slew Rate 구속조건 하에서 제어가 필요하다.

• Journal of Broadcast Engineering
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• v.16 no.5
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• pp.846-860
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• 2011

The binaural auditory system of human has ability to differentiate the direction and the distance of the sound sources by using the information which are inter-aural intensity difference(IID), inter-aural time difference(ITD) and/or the spectral shape difference(SSD). These information is generated from the acoustical transfer of a sound source to pinna, the outer ears. We can create a virtual sound system using the information which is called Head related transfer function(HRTF). However the performance of 3D sound is not always satisfactory because of non-individual characteristics of the HRTF. In this paper, we propose the algorithm that uses human's auditory characteristics for accurate perception. To achieve this, excitation energy of HRTF, global masking threshold and loudness are applied to the proposed algorithm. Informal listening test shows that the proposed method improves the sound localization characteristics much better than conventional methods.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.25-26
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• 2014

배터리를 사용하는 하이브리드 시스템의 확장으로 인하여 2차 전지를 활용할 수 있는 양방향 컨버터의 사용이 증가하고 이에 대한 연구의 필요성 또한 증가하고 있다. 기존 비절연형 단방향 컨버터는 인덕터의 전류와 부하단 캐패시터의 전압을 변수로 지정하고 고정 전원과 고정부하를 대입하여 모델링에 적용했지만, 실제 사용되는 양방향 컨버터의 동작과는 차이가 있다. 또한 이상적인 전원과는 달리 배터리의 단자전압은 SOC 및 충방전 상태에 따라 전압 변동이 일어나고 컨버터의 스위칭 동작에 의해 전압 리플이 발생하기 때문에 제어기를 설계하기 위해서는 이를 반영하여 해석하는 것이 필요하다. 본 논문에서는 비절연형 양방향 컨버터의 양쪽에 부착된 캐패시터가 모두 변수로 적용된 전달함수와 이를 이용하여 설계된 제어기를 제안한다. 컨버터 모델링에 State-Space Averaging 방법을 사용하여 양방향 컨버터의 소신호 분석을 하였고, 충전 모드와 방전 모드 일때 전달함수를 각각 구하였다. 앞서 구한 전달함수를 이용하여 pole/zero 분석을 통해 PI 제어기 설계를 하였고, 주파수 분석을 통해 안정성을 확인하였다.

• 전기의세계
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• v.28 no.12
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• pp.27-32
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• 1979

13명의 환자에 있어서 새로운 비관혈적 방법에 의한 심박출량을 계산하고, 열희석에 의한 방법으로 측정한 심박출량과 비교하였다. 본 논문에서 사용한 비관혈적 펄스 전달 방법은 대동맥 모델에서의 최적 매개변수 방법을 사용하였다. 모델의 최적 매개변수는 맥압의 첫번째 고주파 전달함수에서 측정치와 계산치의 차이를 최소화하는 조건에 의하여 계산하였다. 전달함수의 2개의 펄스는 각각 경동맥동과 대퇴동맥에서 Piezo-resistive Pulse Microphone을 사용하여 측정하였고, 대동맥의 직경은 초음파 방법을 사용하여 측정하였다. 13명의 환자에게서 16가지 측정을 해서 열희석과 비관혈적 방법은 0.89의 상관계수를 보여주었다.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.3 s.43
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• pp.33-42
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• 2005

Frequency domain Volterra model is applied to nonlinear parameter identification procedure for dynamic systems modeled by nonlinear function. The frequency domain Volterra kernels, which correspond io linear, quadratic, and cubic transfer functions in lime domain, are incorporated in nonlinear parametric identification procedure. The nonlinear transfer functions, which can be derived from the Volterra series representation of the nonlinear differential equation of the system by Schetzen's method(1980), are directly used for modeling input output relation. The error is defined by the difference between the observed output and the estimated output which is calculated by substituting the observed input to nonlinear frequency domain model. The system parameters are searched by minimizing the error. Volterra model guarantees enough accuracy and convergence and the estimated coefficients have a good agreement with their actual values not only in the linear frequency region but also in the legion where the $2^{nd}\;or\;3^{rd}$ order nonlinearity is dominant.

• Journal of the Korean Geophysical Society
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• v.5 no.2
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• pp.131-142
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• 2002

Geomagnetic transfer function is generally estimated by choosing transfer to minimize the square sum of differences between observed values. If the error structure sccords to the Gaussian distribution, standard least square(LS) can be the estimation. However, for non-Gaussian error distribution, the LS estimation can be severely biased and distorted. In this paper, the Gaussian error assumption was tested by Q-Q(Quantile-Quantile) plot which provided information of real error structure. Therefore, robust estimation such as regression M-estimate that does not allow a few bad points to dominate the estimate was applied for error structure with non-Gaussian distribution. The results indicate that the performance of robust estimation is similar to the one of LS estimation for Gaussian error distribution, whereas the robust estimation yields more reliable and smooth transfer function estimates than standard LS for non-Gaussian error distribution.