The Journal of the Acoustical Society of Korea (한국음향학회지)

The Acoustical Society of Korea (한국음향학회)
권호 표지
DOI QR코드

DOI QR Code

Analyses on limitations of binaural sound based on the first order Ambisonics for virtual reality audio

1차 Ambisonics에 의해 생성되는 가상현실 오디오용 양이 사운드의 한계에 대한 분석

  • Chang, Ji-Ho (Division of Physical Metrology, Korea Research Institute of Standards and Science) ;
  • Cho, Wan-Ho. (Division of Physical Metrology, Korea Research Institute of Standards and Science)
  • Received : 2019.07.08
  • Accepted : 2019.09.03
  • Published : 2019.11.30
Download PDF
⟨ Previous Next ⟩

Abstract

This paper analyzes the limitations of binaural sound that is reproduced with headphones based on Ambisonics for Virtual Reality (VR) audio. VR audio can be provided with binaural sound that compensates head rotation of a listener. Ambisonics is widely used for recording and reproducing ambient sound fields around a listener in VR audio, and the First order Ambisonics (FOA) is still being used for VR audio because of its simplicity. However, the maximum frequencies with this order is too low to perfectly reproduce ear signals, and thus the binaural reproduction has inherent limitations in terms of spectrum and sound localization. This paper investigates these limitations by comparing the signals arrived at ear positions in the reference field and the reproduced field. An incidence wave is defined as a reference field, and reproduced over virtual loudspeakers. Frequency responses, inter-aural level differences, and inter-aural phase differences are compared. The results show, above the maximum cut off frequency in general, that the reproduced levels decrease, and the horizontal localization can be provided only around the forward direction.

이 논문은 가상현실 오디오에서 널리 사용되는 Ambisonics에 기반하여 헤드폰을 통해 재생하는 binaural sound의 한계를 분석한 것이다. 가상현실 오디오는 청자의 머리 움직임을 보상하는 binaural sound를 통해 제공된다. Ambisonics는 가상현실 오디오에서 청자를 둘러싼 배경음장을 레코딩하고 재생하는데에 널리 사용되는데, 1차 Ambisonics가 간단하다는 장점 때문에 여전히 가상현실 오디오에서 사용되고 있다. 그러나, 물리적인 관점에서 1차의 상한 주파수는 너무 낮아서 귀 위치의 신호를 완벽히 재현하지 못한다. 따라서 이렇게 재생된 binaural sound는 스펙트럼과 음원 위치 형성에서 근본적인 한계를 갖는다. 이 논문은 이러한 한계를 기준 음장과 재생 음장에서의 귀 위치의 신호 비교를 통해 알아 본다. 하나의 입사파를 기준 음장으로 정의하고, 이 것을 가상 스피커를 이용해서 Ambisonics를 통해 재생한다. 주파수 응답, 양이 레벨차, 양이 위상차가 비교된다. 비교 결과, 상한 주파수 이상에서 재생음장의 음압 레벨은 감소하고 수평면 상에서의 음원 위치는 청자의 정면 방향 근처에서만 잘 형성됨을 알 수 있었다.

Keywords

References

  1. P. B. Fellgett, "Ambisonic reproduction of directionality in surround-sound systems," Nature, 252, 534- 538 (1974). https://doi.org/10.1038/252534b0
  2. D. B. Ward and T. D. Abhayapala. "Reproduction of a plane-wave sound field using an array of loudspeakers," IEEE Transactions on speech and audio processing, 9, 697-707 (2001). https://doi.org/10.1109/89.943347
  3. J. Daniel, J. Rault, and J. Polack, "Ambisonics encoding of other audio formats for multiple listening conditions," AES 105th Convention, paper no. 4795 (1998).
  4. M. A. Gerzon and G. J. Barton, "Ambisonic decoders for HDTV," AES 92nd Convention, paper no. 3345 (1992).
  5. F. Zotter and M. Frank, "All-round Ambisonic panning and decoding," J. Audio Eng. Soc. 60, 807-820 (2012).
  6. D. H. Cooper and J. L Bauck, "On acoustical specification of natural stereo imaging," AES 65th Convention, paper no. 1616 (1980).
  7. D. S. Brungart and W. M. Rabinowitz, "Auditory localization of nearby sources. Head-related transfer functions," J. Acoust. Soc. Am. 106, 1465-1479 (1999). https://doi.org/10.1121/1.427180
  8. C. Oreinos and J. M. Buchholz, "Measurement of a full 3D set of HRTFs for in-ear and hearing aid microphones on a head and torso simulator (HATS)," Acta Acustica united with Acustica, 99, 836-844 (2013). https://doi.org/10.3813/AAA.918662
  9. M. A. Gerzon, "Practical Periphony: the reproduction of full-sphere sound," AES 65th Convention. London, UK, paper no. 1571 (1980).
  10. M. A. Gerzon, "The design of precisely coincident microphone arrays for stereo and surround sound," AES 50th Convention, paper no. L-20 (1975).
  11. E. G. Williams, Fourier Acoustics: Sound Radiation and Nearfield Acoustical Holography (Academic press, Cambridge, UK, 1999), pp. 224-227.
  12. M. A. Gerzon, "Periphony: With-height sound reproduction," J. Audio Eng. Soc. 21, 2-10 (1973).
  13. J. Daniel, Representation of acoustic fields, application to the transmission and reproduction of complex sound scenes in a multimedia context, (Doctoral thesis, University of Paris, 2001).
  14. J. Meyer and G. Elko, "A highly scalable spherical microphone array based on an orthonormal decomposition of the soundfield," Proc. IEEE ICASSP. 2, II-1781 (2002).
  15. C. Travis, "A new mixed-order scheme for ambisonic signals," Proc. Ambisonics Symp. 1-6 (2009).
  16. S. Favrot, M. Marschall, J. Kasbach, J. Buchholz, and T. Weller, "Mixed-order ambisonics recording and playback for improving horizontal directionality," AES 131st Convention, paper no. 8528 (2011).
  17. J. -H. Chang and M. Marschall, "Periphony-Lattice mixed-order Ambisonic scheme for spherical microphone arrays," Proc. IEEE/ACM trans. on audio, speech, and lang. 26, 924-936 (2018).
  18. M. Noisternig, A. Sontacchi, T. Musil, and R. Hoeldrich, "A 3D Ambisonic based Binaural Sound Reproduction System," AES 24th Int. Conference on Multichannel Audio, paper no. 1 (2012).
  19. M. Naef, O. Staadt and M. Gross, "Spatialized audio rendering for immersive virtual environments," Proc. the ACM symposium on Virtual reality software and technology. ACM, 65-72 (2002).
  20. A. Solvang, "Spectral impairment of two-dimensional higher order Ambisonics," J. Audio Eng. Soc. 56, 267-279 (2008).
  21. T. McKenzie, D. T. Murphy, and G. Kearney, "Diffusefield equalization of first-order Ambisonics," Proc. the 20th Int. Conf. Digital Audio Effects (DAFx-17), Edinburgh, 5-9 (2017).
  22. T. McKenzie, D. Murphy, and G. Kearney, "Directional bias equalization of first-order binaural Ambisonic rendering," AES Conference on Audio for Virtual and Augmented Reality, paper no. 6-3 (2018).
  23. D. Satongar, C. Dunn, Y. Lam, and F. Li, "Localization performance of higher-order Ambisonics for off-centre listening," BBC Research & Development white paper WHP 254 (2013).
  24. E. M. Benjamin, R. Lee, and A. J. Heller, "Localization in horizontal-only Ambisonic systems," AES 121st Convention, paper no. 6967 (2006).
  25. B. Sebastian and M. Frank, "Localization of 3D ambisonic recordings and ambisonic virtual sources," Proc. 1st Int. Conf. on Spatial Audio, Detmold (2011).
  26. B. Stephanie, J. Daniel, E. Parizet, and O. Warusfel, "Investigation on localisation accuracy for first and higher order ambisonics reproduced sound sources," Acta Acustica united with Acustica, 99, 642-657 (2013). https://doi.org/10.3813/AAA.918643
  27. T. Lewis, C. Armstrong, and G. Kearney, "A Direct comparison of localization performance when using first, third, and fifth Ambisonics drder for real loudspeaker and virtual loudspeaker rendering," AES 143rd Convention, paper no. 9864 (2017).
  28. G. Kearney, M. Gorzel, H. Rice, and F. Boland, "Distance perception in interactive virtual acoustic environments using first and higher order Ambisonic sound fields," Acta Acustica united with Acustica, 98, 61-71 (2012). https://doi.org/10.3813/AAA.918492
  29. M. Gorzel, G. Kearney, and F. Boland, "Investigation of Ambisonic rendering of elevated sound sources," AES 55th Int. Conf. on Spatial Audio, paper no. 5 (2014).
  30. G. Kearney and T. Doyle, "Height perception in Ambisonic based binaural decoding," AES 139th Int. Convention, paper no. 9423 (2015).
  31. J. -H. Chang and W. -H. Cho, "Impairments of binaural sound based on Ambisonics for virtual reality audio," Proc. IEEE 10th Sensor Array and Multichannel Signal Processing Workshop (IEEE SAM), Sheffield, UK, 341-345 (2018).
  32. J. -M. Batke, "The B-format microphone revised," Proc. Ambisonics Symposium, Graz Paper no. 6621 (2009).
  33. S. Spors and J. Ahrens. "Reproduction of focused sources by the spectral division method," Proc. 4th IEEE International Symposium on Communications, Control and Signal Processing (ISCCSP), 1-5 (2010).
  34. V. Pulkki, "Virtual sound source positioning using vector base amplitude panning," J. Audio Eng. Soc. 45, 456-466 (1997).
  35. J. Blauert, Spatial hearing: the psychophysics of human sound localization (MIT press, Cambridge, 1997), pp. 50-137.
  36. D. Colton and R. Kress, Inverse Acoustic and Electromagnetic Scattering Theory, 2nd edition (Springer, New York, 1998), pp. 27.