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2019 Vol.38, Issue 6 Preview Page

Research Article

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

Ji-Ho Chang1∗
,
Wan-Ho Cho1
장 지호1∗
,
조 완호1
1Division of Physical Metrology, Korea Research Institute of Standards and Science
∗Corresponding Author
30 November 2019. pp. 637-650
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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.

Keywords
Binaural reproduction
First order Ambisonics
Virtual reality audio
Inter-aural level difference

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.

키워드
바이노럴 재생
1차 앰비소닉스
가상현실 오디오
양이간 레벨 차이
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Information
  • Publisher :The Acoustical Society of Korea
  • Publisher(Ko) :한국음향학회
  • Journal Title :The Journal of the Acoustical Society of Korea
  • Journal Title(Ko) :한국음향학회지
  • Volume : 38
  • No :6
  • Pages :637-650
  • Received Date : 2019-08-07
  • Accepted Date : 2019-09-03
  • DOI :https://doi.org/10.7776/ASK.2019.38.6.637
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