Acoustic Cues for the Perceptual Assessment of Surround Sound

Speech and audio codecs are implemented in a variety of multimedia applications, and multichannel sound is offered by first streaming or cloud-based services. Beside the objective of perceptual quality, coding-related research is focused on low bitrate and minimal latency. The IETF-standardized Opus codec provides a high perceptual quality, low latency and the capability of coding multiple channels in various audio bandwidths up to Fullband (20 kHz). In a previous perceptual study on Opus-processed 5.1 surround sound, uncompressed and degraded stimuli were rated on a five-point degradation category scale (DMOS) for six channels at total bitrates between 96 and 192 kbit/s. This study revealed that the perceived quality depends on the music characteristics. In the current study we analyze spectral and music-feature differences between those five music stimuli at three coding bitrates and uncompressed sound to identify objective causes for perceptual differences. The results show that samples with annoying audible degradations involve higher spectral differences within the LFE channel as well as highly uncorrelated LSPs.