머리 전달 함수의 보간에 적합한 왜곡 척도 = A Relevant Distortion Criterion for Interpolation of the Head-Related Transfer Functions

국문 초록 (Abstract)

양이 재생 환경에서 다양하고 정확한 공간 이미지 형성을 위해서는 다양하고 세분화된 머리 전달 함수가 요구된다. 방대한 양의 머리 전달 함수를 효과적으로 감축하기 위한 방법으로, 모든 방향에 대한 머리 전달 함수를 몇 개의 대표 값들을 이용해 보간을 통해 얻는 방법이 주로 사용되고 있다. 본 논문에서는 머리 전달 함수의 보간 시 중요한 역할을 하는 보간 왜곡의 측정 방법에 대해 연구하였다. 다양한 객관적 왜곡 측정 방법을 이용하여 보간된 머리전달 함수와 본래의 머리전달 함수 간 차이를 표현하였으며 차이 값과 청취 테스트의 결과를 비교, 분석하였다. 분석 결과로부터 음원의 공간 이미지 차이를 가장 잘 반영하는 객관적 왜곡 측정 방법을 선택하였으며 이를 실제 보간 기법에 적용하였다. 3명의 사람으로부터 측정된 머리전달함수와 1개의 마네킹에서 측정된 머리 전달함수에 제안된 방법을 적용한 결과, 3명의 사람에 대한 머리전달 함수에 대해서는 멜-주파수 켑스트럼 왜곡이, 4 종류의 머리전달 함수에 대해서는 시간 영역의 신호 대 왜곡비자 음원의 공간 이미지 차이를 가장 잘 예측하는 왜곡 척도임을 알 수 있었다.

다국어 초록 (Multilingual Abstract)

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.

참고문헌 (Reference)

1 구교식, "스테레오 시스템을 위한 머리전달함수의 개선" 한국음향학회 27 (27): 207-214, 2008

2 D. D. Rife, "Transfer-Function Measurementsusing Maximum- Length Sequences" 37 (37): 419-444, 1989

3 J. Breebaart, "The perceptual (ir) relevance of HRTF magnitude and phase spectra" 2001

4 J. Blauert, "Spatial Hearing: The Psychophysics of Human Sound Localization" MIT Press 1983

5 W. M. Hartmann, "Signal, sound, and Sensation" Springer 1998

6 A. Kulkarni, "Sensitivity of human subjects to head-related transfer-function phase spectra" 105 (105): 2821-2840, 1999

7 R. Tamura, "Research on the creation of a sound field using a 2- loudspeaker mobile phone" 120-123, 2004

8 A. Kulkarni, "On the minimum -phase approximation of head-related transfer functions" 84-87, 1995

9 C. Avendano, "Modeling the correlated HRTF" 1999

10 R. Luce, "Measurement, scaling and psychophysics. in: Handbook of Experimental Psychology" Wiley 1988

11 R. Nicol, "Looking for a relevant similarity criterion for HRTF clustering: a comparative study" 2006

12 MIT media lab, "KEMAR HRTF data"

13 J. R. Deller, "Discrete-Time Processing of Speech Signals" Macmillan Publishing Company 1993

14 P. Minnaar, "Directional resolution of head-related transfer functions required in binaural synthesis" 53 (53): 919-929, 2005

15 F. Keyrouz, "A new HRTF interpolation approach for fast synthesis of dynamic environmental interaction" 56 (56): 28-35, 2008

16 D. Kistler, "A model of head-related transfer functions based on principal components analysis and minimum-phase reconstruction" 91 (91): 1637-1647, 1992

17 S. Shimada, "A clustering method for sound localization transfer functions" 42 (42): 577-584, 1994