• The Journal of the Acoustical Society of Korea
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• v.30 no.4
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• pp.167-180
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• 2011

Recently, 3-D audio technologies are commonly implemented through headphones. A major problem of the headphone-based 3-D audio is in-the-head localization, which occurs due to the inaccurate Head-Related Transfer Function (HRTF). Since the individual measurements of HRTFs are impractical, there have been several researches for HRTF customization. In this paper, an efficient method of customizing HRTFs for the sound externalization is proposed. Firstly, it is determined which part will be customized in HRTF through psychoacoustical experiments. Then, the method controlling spectral notches and envelopes to provide individual localization cues are described. Since the proposed method is based on a critical-band rate, the structure is much simpler than that of previous studies, but still effective. The performance was evaluated through a series of subjective tests, and the results confirmed that the customized HRTF using proposed method could replace the measured individual HRTF successfully.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.06a
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• pp.58-59
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• 2013

임의의 위치에 음상을 정위하는 기초적인 방법으로, 각각의 고도각과 방위각에서 측정된 머리전달함수를(HRTF : Head Related transfer Function) 원음에 convolution하는 기법이 사용된다. 하지만 더미헤드를 통해 측정된 HRTF는 사용자에 따라 정위감을 저하시킬 수 있다. 또한 좌표로 표현되는 영상과는 달리, 소리는 들려오는 방향을 정확한 좌표로 표현하기가 힘들다. 이에 본 논문은 HRTF를 사용하여 음상을 정위하는 경우의 정위감 개선에 대한 방법을 제안한다. 정위감 개선을 위해 Neville 보간법을 통해 HRTF를 그룹화하는 방법에 대해 연구하였으며, 생성된 HRTF를 음상 정위에 사용하고 청감 평가를 통해 성능을 확인하였다.

• Proceedings of the Korea Multimedia Society Conference
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• 2003.11a
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• pp.334-337
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• 2003

입체음향을 구현하는 방법에는 5 혹은 6 개의 스피커를 사용하는 5.1 채널 음향재생 시스템과 2개의 스피커를 사용하는 방법있다. 2 채널 입체음향재생 시스템은 라우드 스피커 재생보다 헤드폰 재생에 사용되고 있다. 2 채널로 입체음향을 재생하기 위하여 사람의 머리와 귀바퀴를 FIR 필터로 모델링한 머리전달함수(HRTF, head related transfer function)을 이용한다. FIR 필터로 측정된 HRTF는 실시간 처리에 있어서 계산량이 많은 단점이 있다. 본 논문에서는 2 채널 입체 음향시스템을 효과적으로 구현하기 위하여 FIR HRTF를 HR필터로 구현하는 방법을 제안한다. FIR 필터계수로부터 IIR 필터계수를 구하는 알고리즘은 균형화 모델 감소법(balanced model reduction)을 이용한다. 본 논문에서는 IIR 필터로 차수를 줄인 HRTF로 입체음향을 재생하는 시뮬레이션을 하였다.

• The Journal of the Acoustical Society of Korea
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• v.20 no.6
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• pp.94-103
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• 2001

The goal of using numerical methods in this study is two-fold: to replicate a set of measured, individualized HRTFs by a computer simulation, and also to visualise the resultant sound field around the head. Two methods can be wed: the Boundary Element Method (BEM) and the Infinite-Finite Element Method (IFEM). This paper presents the results of a preliminary study carried out on a KEMAR dummy-head, the geometry of which was captured with a high accuracy 3-D laser scanner and digitiser. The scanned computer model was converted to a few valid BEM and IFEM meshes with different polygon resolutions, enabling us to optimise the simulation for different frequency ranges. The results show a good agreement between simulations and measurements of the sound pressure at the blocked ear-canal of the dummy-head. The principle of reciprocity provides an effect method to simulate HRTF database. The BEM was also used to investigate the total sound field around the head, providing a tool to visualise the sound field for different arrangements of virtual acoustic imaging systems.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 2000.04a
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• pp.76-80
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• 2000

본 논문은 입체 음상 정위 시스템에 있어서 청취자의 머리 크기와 음상 정위를 원하는 위치와의 거리에 따른 머리전달함수 (HRTF; Head Related Transfer Function)의 보정 방법에 관한 것이다. 제안된 방법은 먼저 표준 반경에서 표준 머리 크기의 더미 헤드를 이용해 측정된 표준 머리전달함수 데이터베이스로부터 실제의 왼쪽 또는 오른쪽 귀를 기준으로 한 방위각과 고도각을 산출한다. 이렇게 산출된 방위각과 고도각을 기준으로 머리전달함수 데이터베이스의 인덱스를 보정한다. 음상 정위하고자 하는 3차원 공간상의 위치를 입력받게 되면, 입력받은 위치로부터 청취자의 왼쪽 또는 오른쪽 귀를 기준으로 한 방위각과 고도각을 산출한 후에 보정된 머리전달함수 데이터베이스로부터 머리전달함수를 가져와서 입력 모노 신호를 보정된 머리전달함수와 콘볼루션하여 입체음향을 생성하게 된다.제안된 방법에 의해 청취자의 머리 크기 및 거리에 따라 보정된 머리전달함수를 사용함으로써 청취자에게 보다 실감나는 3차원 음상 정위 효과를 제공할 수 있다.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.338-344
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• 2017

In this paper, an interpolation method of HRTF (Head-Related Transfer Function) is proposed for small-sized measurement data set, especially. The proposed algorithm is based on acoustic modeling of HRTFs, and the algorithm tries to interpolate the HRTFs via estimation the model coefficients. However, the estimation of the model coefficients is hard if there is lack of measurement points, so the algorithm solves the problem by a data augmentation using the VBAP (Vector Based Amplitude Panning). Therefore, the proposed algorithm consists of two steps, which are data augmentation step based on VBAP and model coefficients estimation step by least squares method. The proposed algorithm was evaluated by a simulation with a measured data from CIPIC (Center for Image Processing and Integrated Computing) HRTF database, and the simulation results show that the proposed algorithm reduces mean-squared error by 1.5 dB ~ 4 dB than the conventional algorithms.

• 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.

• Proceedings of the IEEK Conference
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• 2003.07e
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• pp.2140-2143
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• 2003

최근 게임, 멀티미디어 콘텐츠, 가상현실 둥을 제공하는 멀티미디어 장치에서 2 개의 스피커나 헤드폰을 이용하여 3 차원 입체 음향효과를 내고자 하는 가상 입체음향 기법에 관한 연구가 많이 이루어지고 있다 가상 입체음향 기법 중 다채널 입체음향을 이용하여 입체음향효과를 가진 2 채널 출력을 구성하는 방식의 대표적인 것으로는 입체음향 정위효과를 내는 HRTF(Head Related Transfer Function)이 있다. 그러나 이 방법은 전달함수와 입력 신호의 컨볼루션(Convolution)방법을 이용함으로써 계산량이 복잡하여 실시간 구현에 많은 제약을 주고 있다. 본 논문에서는 다채널 입력으로 현재의 DVD, HDTV 등에서 사용되는 Dolby-Digital 복호화기를 사용하여 입체음향 시스템을 구현할 경우 가상입체음향 신호처리에 사용되는 HRTF 계수를 MDCT 계수로 구성하여 이를 통한 가상입체음향 신호처리방식의 계산량 감소방법에 대하여 설명하고 있다.

• Journal of Advanced Navigation Technology
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• v.15 no.2
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• pp.326-333
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• 2011

In the present study, we measured the performance (accuracy and reaction time) of the user in the virtual environment with see-through Head-Mounted Display system that includes 3D sound generated through Head-Related Transfer Function (HRTF) to investigate the feasibility of auditory display for a certain object's spatial information. To sum up the results of two experiments, when presenting location information of the object with 3D sound, it is desirable that information arrangement from the user should be an orthogonal pattern which is located with right angle, not a diagonal pattern. Like these results propose that spatial information presentation with 3D sound make the optimal object arrangement of virtual environment possible.

• The Transactions of the Korea Information Processing Society
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• v.7 no.5
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• pp.1361-1369
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• 2000

For the implementation of 3D Sound Localization system, the binaural filtering by HRTFs is generally employed. But the HRTF filter is of high order and its coefficients for all directions have to be stored, which imposes a rather large memory requirement. To cope with this, research works have centered on obtaining low dimensional HRTF representations without significant loss of information and synthesizing the original HRTF efficiently, by means of feature extraction methods for multivariate dat including PCA. In these researches, conventional linear PCA was applied to the frequency domain HRTF data and using relatively small number of principal components the original HRTFs could be synthesized in approximation. In this paper we applied neural network based nonlinear PCA model (NLPCA) and the nonlinear PLS repression model (NLPLS) for this low dimensional HRTF modeling and analyze the results in comparison with the PCA. The NLPCA that performs projection of data onto the nonlinear surfaces showed the capability of more efficient HRTF feature extraction than linear PCA and the NLPLS regression model that incorporates the direction information in feature extraction yielded more stable results in synthesizing general HRTFs not included in the model training.