Perceptual differences caused by altering the elevation of early room reflections
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Examensarbete för masterexamen
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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.
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Ämne/nyckelord
spatial audio, auditory perception, psychoacoustics, elevated reflections, spatial decomposition method, room acoustics, spatial impulse responses, loudspeaker array, microphone array, direction of arrival