Abstract: A head related transfer function (HRTF) is used to simulate positional three-dimensional sound. The HRTF accounts for the frequency response, delays and reflections of the human body. The HRTF is unique to each individual and is affected by the shape and size of the head, the shape and size of the pinnae, the characteristics of the ear canal and the relationships of the shoulder to the ear. An HRTF for an individual is interactively approximated by first choosing a generalized HRTF. A computer, or other device, outputs audio signals from fixed locations using the generalized HRTF. Although the sound is output from fixed positions, a user may be expected to perceive the sound from a position different than the fixed position from which the sound is output. The user inputs the actual perceived position of the sound to the computer. The computer calculates positional errors between the expected perceived position of the sound and the actual perceived position of the sound.