A method and apparatus for producing virtual sound sources that are externally
perceived and positioned at any orientation in azimuth and elevation from a listener
is described. In this system, a set of speakers is mounted in a location near the
temple of a listener's head, such for example, on an eyeglass frame or inside a
helmet, rather than in earphones. A head tracking system determines the location
and orientation of the listener's head and provides the measurements to a computer
which processes audio signals, from a audio source, in conjunction with a head
related transfer function (HRTF) filter to produce spatialized audio. The HRTF
filter maintains the virtual location of the audio signals/sound, thus allowing
the listener to change locations and head orientation without degradation of the
audio signal. The audio system of the present invention produces virtual sound
sources that are externally perceived and positioned at any desired orientation
in azimuth and elevation from the listener.