Fast head-related transfer function measurement via reciprocity

Abstract

An efficient method for head-related transfer function (HRTF) measurement is presented. By applying the acoustical principle of reciprocity, one can swap the speaker and the microphone positions in the traditional (direct) HRTF measurement setup, that is, insert a microspeaker into the subject's ear and position several microphones around the subject, enabling simultaneous HRTF acquisition at all microphone positions. The setup used for reciprocal HRTF measurement is described, and the obtained HRTFs are compared with the analytical solution for a sound-hard sphere and with KEMAR manikin HRTF obtained by the direct method. The reciprocally measured sphere HRTF agrees well with the analytical solution. The reciprocally measured and the directly measured KEMAR HRTFs are not exactly identical but agree well in spectrum shape and feature positions. To evaluate if the observed differences are significant, an auditory localization model based on work by J. C. Middlebrooks [J. Acoust. Soc. Am. 92, 2607-2624 (1992)] was used to predict where a virtual sound source synthesized with the reciprocally measured HRTF would be localized if the directly measured HRTF were used for the localization. It was found that the predicted localization direction generally lies close to the measurement direction, indicating that the HRTFs obtained via the two methods are in good agreement.

Using Virtual Acoustic Space to Investigate Sound Localisation

“…However, it is also possible to take the reverse approach, that is, placing the sound source into the ear canal and record the signal that is arriving at a microphone after filtering by the ear canal and outer ear (e.g. Zotkin et al, 2006). The microphones that record the output signals are then positioned at the exact spatial locations where usually the loudspeaker would be.…”

A framework for geometry acquisition, 3-D printing, simulation, and measurement of head-related transfer functions with a focus on hearing-assistive devices

“…In the simulation, the reciprocal approach was used [13,35]: the sound source was placed at the microphone position, and the sound pressure level was calculated on a sphere surrounding the head at 1.2 m distance. The reciprocal approach yields equivalent results to the direct approach, but the simulation can be performed for all sound-source directions in a single simulation step [36].…”

“…Listener-specific HRTFs are often acoustically measured by placing small microphones at the entrance of the listener's ear canals. During a measurement session, often consisting of measurements for many spatial positions, the listener must sit still for tens of minutes depending on the measuring facilities [12][13][14]. Thus, it is not surprising that in some applications, generic HRTFs, i.e., HRTFs of a manikin representing an average of the human population [15][16][17], are used.…”

Reexamination of fast head-related transfer function measurement by reciprocal method

“…A fast HRTF measurement method using the Helmholtz reciprocity principal proposed by Zotkin et al can overcome this problem [2]. The reciprocal method is used to measure HRTFs by placing a miniature speaker in the ear and microphones around the head.…”