The transfer function imposed on sound arriving at the two ears of a listener due to the physical dimensions and shape of the upper torso and head. The HRTF is unique to an individual listener. The binaural HRTF is the left and right ear frequency response to a sound source at a particular position, and in practice a set of binaural HRTF measurements would usually be made for a sound source placed at a number of positions on a sphere around the head of a listener or a dummy head. Ideally, such measurements should be made in an anechoic room where the walls, floor, and ceiling absorb sound energy fully so that none is reflected back into the space.