Auditory Localization in Low Bitrate Compressed Ambisonic Scenes
Abstract
The increasing popularity of Ambisonics as a spatial audio format for streaming services
poses new challenges to existing audio coding techniques. Immersive audio delivered to mobile
devices requires an efficient bitrate compression that does not affect the spatial quality of the
content. Good localizability of virtual sound sources is one of the key elements that has to be
preserved. This study was conducted in order to investigate the localization precision of virtual
sound source presentations within Ambisonic scenes encoded with Opus low bitrate compression at
different bitrates and Ambisonic orders (1st, 3rd, and 5th). The test stimuli were reproduced over
a 50-channel spherical loudspeaker configuration and binaurally using individually measured and
generic HRTFs. Participants were asked to adjust the position of a virtual acoustic pointer to match
the position of virtual sound source within the bitrate compressed Ambisonic scene. Results show that auditory localization in low bitrate compressed Ambisonic scenes is not significantly affected by
codec parameters. The key factors influencing localization are the rendering method and Ambisonic
order truncation. This suggests that efficient perceptual coding might be successfully used for mobile
spatial audio delivery.