Front-and-Overhead Energy Ratio and immersive sound field rendering with height channels

In a discrete channel-based music reproduction, height channels are required to completely manipulate increased immersiveness and enhanced appropriateness for a realistic three-dimensional (3D) sound field. Previous subjective evaluation results showed that the configuration of four height loudspeakers significantly changed perceived immersiveness and appropriateness, and the listeners preferred height-loudspeaker configurations with being “frontal” and “full.” Subsequent analysis failed to determine a prediction model that could account for the variation of the listeners’ perceptual responses using conventional physical parameters including inter-aural difference and coherence. In this paper, the authors proposed a new metric-the ratio between sound energy from front and overhead directions-as a physical parameter for the prediction model. A coincident pair of bidirectional microphones (one facing front and the other facing overhead) measured acoustical impulse responses (IRs) at the listening position for eight configurations of four height channels. Subsequent analysis measured the Front-and-Overhead Energy Ratio (FOER) between two IRs from the eight configurations and found that the ratios were highly correlated with the listeners’ subjective rank data on perceived immersiveness and appropriateness (r = -0.8037). The result implicated that the appropriated configuration of height channels is a critical factor to render a convincing and immersive 3D sound field due to its direct influence on the FOER.