This study examines several different methods for measuring objective differences between 3D audio reproduction conditions with and without bottom channels (floor-level loudspeaker channels) within 9+10+8 audio reproduction. The methods, derived from previous studies investigating 2D and 3D audio reproduction, examine mono and binaural signal features, as well as various ratios of directional sound energy. Stimuli were created using short excerpts of seven different 3D audio recordings covering a range of musical and non-musical sound scenes and audio recording methods. Three different reproduction conditions were examined: 1) all vertical loudspeaker layers active, 2) bottom-layer signals muted), and 3) downmix: bottom-layer signals and main-layer signals merged, across three different acoustic environments: a large mixing studio, a small mixing studio, and a hemi-anechoic room. In this study, most measurement techniques under test did not yield meaningful results. However, averaged power spectra measurements show a consistent trend towards greater low frequency energy when the bottom-layer loudspeaker channels are active. Possible alternative measurement techniques are discussed.
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