### ASA 124th Meeting New Orleans 1992 October

## 1aPP6. Investigation of phase distortion in the synthesis of head-related
transfer functions.

**Michael A. Blommer
**

**
Gregory H. Wakefield
**

**
**
*Dept. of Elec. Eng. and Comput. Sci., 1301 Beal Ave., Univ. of Michigan,
Ann Arbor, MI 48109-2122
*

*
*
Synthesizing over headphones the free-field to ear-canal transfer
functions, or head-related transfer functions (HRTFs), of the human auditory
system poses several difficulties from the standpoint of digital signal
processing. Since the order of the HRTF is unknown, it is necessary to assume a
particular value when estimating the HRTF from responses obtained in an
anechoic chamber. Additionally, while standard filter designs minimize the
squared error between the desired and designed response, applications such as
HRTF synthesis are likely to require error metrics that are sensitive to
disparities between the log magnitude response of each system. A new design
algorithm is proposed that is based on a logarithmic distortion metric and it
is shown how this algorithm can be used to obtain minimum phase, low-order
pole-zero approximations to HRTFs. Psychophysical results characterizing
audibility sensitivity to such HRTF approximation errors are presented in order
to establish an audible limit for the distortion in such designs. These results
are compared with similar experimental results for the widely used
least-squares metric. [Research supported by a grant from the NIDCD of the
National Institute of Health.]