Abstract
Ambisonics is a spatial audio technique appropriate for dynamic binaural rendering due to its sound field rotation and transformation capabilities, which has made it popular for virtual reality applications. An issue with low-order Ambisonics is that interaural level differences (ILDs) are often reproduced with lower values when compared to head-related impulse responses (HRIRs), which reduces lateralization and spaciousness. This paper introduces a method of Ambisonic ILD Optimization (AIO), a pre-processing technique to bring the ILDs produced by virtual loudspeaker binaural Ambisonic rendering closer to those of HRIRs. AIO is evaluated objectively for Ambisonic orders up to fifth order versus a reference dataset of HRIRs for all locations on the sphere via estimated ILD and spectral difference, and perceptually through listening tests using both simple and complex scenes. Results conclude AIO produces an overall improvement for all tested orders of Ambisonics, though the benefits are greatest at first and second order.
Highlights
The human auditory system can determine the direction and distance of incoming sounds using three primary binaural localization cues: interaural time difference (ITD), interaural level difference (ILD), and spectral cues
This paper presents a method for addressing the inadequate ILD reproduction of low-order binaural Ambisonic rendering using virtual loudspeakers through a pre-processing stage of the head-related impulse responses (HRIRs) used in the binaural rendering of Ambisonic signals
In most cases this comes in the form of an increase in ILD, but not all - some places show Ambisonic ILD Optimization (AIO) reduces ILD of the Ambisonic rendering
Summary
The human auditory system can determine the direction and distance of incoming sounds using three primary binaural localization cues: interaural time difference (ITD), interaural level difference (ILD), and spectral cues. ITDs and ILDs are based on the difference in signals arriving at the left and right ears and help determine the horizontal direction of the sound. Spectral cues are caused by acoustic perturbations such as diffraction and reflections off and around the torso, head and pinnae, and help determine the vertical direction of the sound. Other factors that contribute to a realistic spatial audio experience are externalization and spaciousness. Lower interaural correlation has been shown as necessary to elicit the feeling of spaciousness [1]. Higher values of ITD and ILD will improve spaciousness
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