IR/(dynamic) HRTF/DRTF-Acquisition
Continuous-Azimuth HRTF Measurement
Head-Related Transfer Functions (HRTFs) describe the direction-dependend acoustic influence of a person's torso, head and pinna on the sound received at the ear canal. They are widely used in virtual reality applications. As the acoustic properties of torso, head and pinna vary noticeably between different persons, a fast and cost-effective measurement of individual HRTFs is desirable.
Adaptive filtering approaches can be used for the fast measurement of azimuth-continuous HRTFs. The subject or dummy head to be measured is rotated during the continuous measurement at a constant angular speed. Afterwards, the HRTFs measured at different times can be determined using a system identification algorithm and related to different directions by the known rotation.
Acoustical Head-Tracking
Continuous HRTF measurement can be made more flexible by allowing subjects to move freely during the measurement and recording these movements. Acoustical headtracking is particularly well suited for this application [Nagel18]. A microphone array is mounted to the head of the subject. The current head orientation is determined from the microphone array signals.
Advantages of acoustical head-tracking compared to other head-tracking methods include
- Arbitrary 3D head movements are possible
- Purely acoustical measurement requires no synchronisation between different types of sensors
- Coordinate systems and loudspeaker position are implicitly calibrated
Excitation Signals for Dynamic Measurements
The difference between acoustic measurements and other applications of system identification is that the excitation signal x(k) for a measurement can be chosen. For measurements of time-variant systems, such as the HRTF measurements, the group delay of the excitation signal has significant influence on the tracking of system changes [Kühl18a]. Specifically designed excitation signals or appropriate post-processing measures can be used to minimize audible artifacts in the measured impulse responses.
References
[Kühl18a]
Stefan Kühl, Sebastian Nagel, Tobias Kabzinski, Christiane Antweiler, and Peter Jax
Tracking of Time-Variant Linear Systems: Influence of Group Delay for Different Excitation Signals
International Workshop on Acoustic Signal Enhancement (IWAENC), September 2018
[Nagel18]
Sebastian Nagel, Tobias Kabzinski, Stefan Kühl, Christiane Antweiler, and Peter Jax
Acoustic Head-Tracking for Acquisition of Head-Related Transfer Functions with Unconstrained Subject Movement
AES International Conference on Audio for Virtual and Augmented Reality (AVAR), August 2018
[Enzner13]
Gerald Enzner, Christiane Antweiler, and Sascha Spors
Trends in Acquisition of Individual Head-Related Transfer Functions
in: The Technology of Binaural Listening, Jens Blauert (ed.), Springer-Verlag Berlin Heidelberg, June 2013
[Antweiler11]
Christiane Antweiler and Peter Vary
Sequential and Direct Access of HRTFs for Quasi-Continuous Angular Positions
European Signal Processing Conference (EUSIPCO), August 2011
[Antweiler09]
Christiane Antweiler and Gerald Enzner
Perfect Sequence LMS For Rapid Acquisition Of Continuous-Azimuth Head Related Impulse Responses
IEEE Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA), October 2009