Perceptual differences caused by altering the elevation of early room reflections

Abstract

In recent years, spatial audio became more and more relevant for consumer applications such as immersive multimedia playback and video games. Thereby, an ongoing challenge is to authentically reproduce the spatial auditory impression of acoustic spaces. In this context, it has not yet been investigated how accurately the vertical positions of early reflections need to be reproduced in order to result in a plausible spatial room impression. The aim of this thesis is to evaluate the ability of the human hearing system to distinguish between early reflections with different elevation angles as well as to quantify the auditory differences caused by changing an early reflection’s elevation. Therefore, impulse responses of an isolated ceiling reflection were measured and, in combination with spatial impulse responses of two different rooms, used to perform both loudspeaker- and headphone-based listening experiments. The results of these experiments show that changing an early reflection’s elevation angle can lead to clearly perceivable differences depending on the reflection strength, the reflection position, the change in elevation, the acoustic environment and the source signal. Thereby, the loudspeaker based reproduction method with custom HRTFs resulted in larger perceived spatial differences than the headphone based method using generalized HRTFs. Furthermore, it was found that the change in interaural cross-correlation caused by altering a reflection’s elevation angle is strongly related to the amount of perceived spatial differences. The outcomes of this thesis suggests that, under certain conditions, the vertical positions of early reflections need to be reproduced in order to achieve an authentic spatial room impression. On the other hand, it was shown that compressing all elevated reflections of a spatial room impulse response to the horizontal plane does not result in perceivable differences if the SRIR is sufficiently diffuse and does not contain pronounced ceiling reflections.