In the general context of three-dimensional sound synthesis based on head-related transfer functions (HRTFs), the spatial resolution of the available HRTFs is of significant importance in terms of the perceived quality of the synthesized sound. If the spatial resolution is too low, it is likely that spatial perception is degraded. This can be overcome by the use of a higher resolution. However, using a resolution higher than the spatial resolution of the human auditory system will not bring any further improvement, and it might actually become a waste of resources. This project investigates how well humans discriminate differences between HRTFs, and what the minimum directional difference is, for which we can perceive a difference of any kind. The discrimination of differences in the spectral and temporal characteristics of the HRTFs is studied separately. Psychophysical experiments are used in order to measure two thresholds defined as the minimum audible spectral difference (MASD) and the minimum audible time difference (MATD) of HRTFs. A separate project investigates the audibility of switching between HRTFs for dynamic three-dimensional sound synthesis (Audibility thresholds for HRTF-switching in binaural synthesis). Supported by STVF/FTP.