A system for customising the synthesis and generation of spatial hearing in virtual auditory space (VAS) for individual listeners includes a measuring ruler (12) and a digital processing unit (DPU) (14) to which the ruler (12) is connected. The ruler (12) is used for measuring various physical dimensions of the morphology of a person's external auditory periphery (16). The ruler (12) comprises a base (18) insertable into an ear canal (20) of the person's ear. A robotic measuring arm (22) extends from the base (18) and has a measuring tip (24) to enable the ruler (12) to record the Cartesian (x,y,z) coordinates of the tip (24) relative to the base (18). By suitable manipulation of the robotic arm (22), the tip (24) can be positioned at desired locations on the person's external auditory periphery (16) to enable the morphological measurements of the person's external auditory periphery (16) to be effected. The ruler (12) is electrically connected via a lead (26) to the DPU (14) which is programmed to compute either head related transfer function (HRTF) filter coefficients or HRTF spectral weights. Functional relationships may thus be used to generate, by means of the DPU (28), HRTFs at any location for any individual listener given an encoding of the individual listener's morphological measurements.