Perceptual Comparison of 3D Audio Reproduction With and Without Bottom Channels

This study examines the perceptual effects of bottom channels, i.e., floor-level loudspeakers, within 3D audio reproduction. Two listening tests were undertaken at three different venues, using experienced subjects. Both experiments involved comparing three different versions of seven different musical and nonmusical sound scenes: the original mix with all three vertical loudspeaker layers active (Full), the bottom layer muted (Cut), and the bottom layer down-mixed into the main layer loudspeakers (X). Results indicate that listeners could discriminate between the three reproduction conditions with a very high degree of accuracy, particularly when comparing the "Full vs. Cut" and "Full vs. X" conditions. Subjects found that the most salient aspects of the sound scene in terms of differentiating between reproduction conditions were related to low-frequency energy, changes in horizontal and vertical imaging, and timbre/tone. Discrimination ability between reproduction conditions was consistent across all three listener groups, though subjects' perception of the degree of difference between reproduction conditions across various auditory attributes varied between groups. These differences may be related to subjects' previous experience with 3D audio including bottom channels, venue bottom-layer loudspeaker angles of elevation, and venue acoustic conditions.