Augmentation of perceived spatial extent of reverberation in stereophonic listening using elevation filters

Perception-based elevation filters allow illusory sound source elevation in loudspeaker listening. The filters are applied to early-reflection parts of two-channel stereophonic room impulse responses to augment spatially the perception of the reverberant field. Two types of elevation filters are applied to the early reflections, both targeting 60 ^◦ elevation: a frequency-weighting filter based on Blauert’s directional band theory and a difference-spectrum filter. A listening test examines the effect on perceived spatial ‘extension’ and spectral ‘colouration’ compared to the unfiltered reference stimulus. The results show that the elevation filters extend the auditory space slightly, and the perceived colouration by those filters is within an acceptable level. However, a higher extension level tends to yield more prominent colouration. Additionally, elongated reverberation time or amplified early reflection levels result in a more significant extension, allowing control of the elevation filter applications to a desired extension level while restraining colouration to a tolerable level.