The goal of a music playback system is to reproduce as closely as possible the sound experience of live music. Despite the excellent frequency response afforded by smaller, lighter transducers, headphones produce an unnatural “in the head” sound experience that many acute listeners find distracting.
Head-related transfer functions (HRTFs) are an individualized summarization of the direction-dependent acoustic filtering a free-field sound undergoes due to a person’s head, torso, and pinna varying as a function of source position and having large intersubject variation. The common acoustical pole and zero (CAPZ) model requires far fewer variable parameters to represent HRTFs. In this study, different approximations of the CAPZ model are processed and evaluated in their ability to emulate the external sound field of loudspeakers while headphones are worn.
The subjective results show that there was no audible drop in quality when HRTFs were incorporated to the sound and that no approximation was singled out as having the best sound quality, but it was observed that the amount of balance between the poles and zeros had an audible effect to the listeners.