Use of a common-acoustical-pole and zero model is proposed for modeling hea
d-related transfer functions (HRTF's) for various directions of sound incid
ence. The HRTF's are expressed using the common acoustical poles, which do
not depend on the source directions, and the zeros, which do, The common ac
oustical poles are estimated as they are common to HRTF's for various sourc
e directions; the estimated values of the poles agree well with the resonan
ce frequencies of the ear canal. Because this model uses only the zeros to
express the HRTF variations due to changes in source direction, it requires
fewer parameters (the order of the zeros) that depend on the source direct
ion than do the conventional all zero or pole/zero models. Furthermore, the
proposed model can extract the zeros that are missed in the conventional m
odels because of pole-zero cancellation. As a result, the directional depen
dence of the zeros can be traced well. Analysis of the zeros for HRTF's on
the horizontal plane showed that the nonminimum-phase zero variation was we
ll formulated using a simple pinna-reflection model, The common-acoustical-
pole and zero (CAPZ) model is thus effective for modeling and analyzing HRT
F's.