A method to process audio signals, an apparatus accepting audio signals, a
carrier medium that carried instructions for a processor to implement the
method to process audio signals, and a carrier medium carrying filter
data to implement a filter of audio signals. The method includes
filtering a pair of audio input signals by a process that produces a pair
of output signals corresponding to the results of: filtering each of the
input signals with a HRTF filter pair, and adding the HRTF filtered
signals. The HRTF filter pair is such that a listener listening to the
pair of output signals through headphones experiences sounds from a pair
of desired virtual speaker locations. Furthermore, the filtering is such
that, in the case that the pair of audio input signals includes a panned
signal component, the listener listening to the pair of output signals
through headphones is provided with the sensation that the panned signal
component emanates from a virtual sound source at a center location
between the virtual speaker locations.