Controlling the Head Position during individual HRTF Measurements and its Effect on Accuracy

The head-related transfer function (HRTF) describes the incident direction and frequency dependent representation of sound at the eardrum of a listener, caused by transmission effects of the specific outer ear, head and torso. It is an individual ”fingerprint” that we are used to hear the world through, and when the HRTF of a subject is known, persuading simulation of free-field listening can be achieved by processing a signal with the HRTF prior to presentation over headphones [1]. When measuring HRTFs, one source of error is movement of the subject, particularly the head, causing the effective sound incident direction to dynamically deviate from the desired one. Such movement is inevitable and occurs even if the subjects are instructed to remain still, and do in their subjective impression. Commonly, this source of inaccuracy is addressed by providing a headrest or similar mechanic support, which however cannot avoid such movement completely [2–6]. In this work, a novel method for both recording and interactively controlling the head position based on visual feedback is presented. The approach was successfully implemented and applied in individual HRTF measurements, where repeated rounds of measurements were conducted and a stable subject position was particularly crucial. The results show that excellent control over the head position and orientation is achieved, and the connected residual influence on the obtained HRTFs is in a negligible size.