Head-related transfer functions (HRTFs) are an essential part of 3D headphone audio. OwnSurround has developed a simulation based service for the fast generation of personalized HRTFs.

1. HRTF Service for Professionals
2016

2. In a nutshell
• Simulation based service for high-resolution HRTF acquisition
• Full control of Head-and-Torso (HAT) model and environment:
• Ideal point sources/receivers at exact locations
• Perfectly anechoic environment
• Easiness of geometric changes (CAD model)
• Freely adjustable surface impedances
• Superior spatial resolution
• Easily utilization of results in the SOFA-format

3. Scan, simulate and listen


OwnSurround uses full-wave cloud
computing technology for the fast
simulation of the HRTF

4. Challenges in HRTF measurements
• Inter-measurement variability
“Results revealed spectral magnitude variations up to 12.5 dB for
frequency bands below 6 kHz and up to 23 dB above that.”
“Nevertheless, the observed ITD variations of up to 235 sec are alarming as
they often exceeded reported JND values. Such findings highlight
the potential impact of physical spaces, measurement routines,
and equipment types on the collected HRTF data.”*
• Inaccurate in near-field
“Note, that for the distance of 0.5m the used Genelec loudspeaker presents
not really a point source. In addition, the HRTFs for 0.5m include reflections
of the sound going from the KEMAR head back to the loudspeaker and back
to the dummy head.”**
*Andreopoulou et al: Inter-Laboratory Round Robin HRTF
Measurement Comparison, IEEE JOURNAL OF SELECTED
TOPICS IN SIGNAL PROCESSING, VOL. 9, NO. 5, 2015
**http://twoears.aipa.tu-berlin.de/doc/1.2/database/impulse-
responses/#anechoic-measurements-hrtfs

5. Simulated HRTFs
• “… virtualisation by using the simulated HRTFs is
preferred over virtualisation by the measured HRTFs …”*
• Fast boundary element solution
of the acoustic wave equation**
• The HRTF is solely defined by
the geometry of model and surface
impedances
full control of accuracy
*Turku et al: Perceptual evaluation of numerically simulated Head-Related
Transfer Function, AES 124th Convention, 2008.
**Huttunen et al: Rapid generation of personalized HRTFs, AES 55th
International Conference: Spatial Audio, 2014.

6. High accuracy
• Increased spatial and spectral resolution
• Simulations can be easily computed for thousands of sound
directions (e.g. one degree spacing in both azimuth and
elevation)
• High spectral resolution (e.g. 32 - 24 000 Hz in 32Hz steps)
• Near-field HRTFs (eg. close to ear sources)
• Ideal point sources guarantee the high accuracy in near-
field

7. 3d surface mesh
• The simulation needs a
triangulated surface mesh
for the head and torso
• Obtained using 3d
scanning:
• Structured light scanning
• Photogrammetry
• Laser scanning
• Well-known
requirements for
resolution*:
• <2mm on pinna
• <5mm elsewhere*Ziegelwanger et al: Numerical calculation of listener-specific head-related transfer functions and sound
localization: Microphone model and mesh discretization, The Journal of the Acoustical Society of America, vol 138,
no 1, pp. 208-222, 2015

8. Pinna
• A key role in personalized
HRTFs
• Visibility of 3d scanning to
the entrance of the ear-canal
Simulation corresponds
to blocked ear measurements

9. 3d scanning
• Use a local 3d scanning service
• OwnSurround provides a scanning guide
• Scanning service by OwnSurround
• At your own premises

10. Input data
• The mesh (e.g. in STL-format)
• Customizable parameters (default values in parenthesis):
• Frequencies (64 - 24000Hz in 64 Hz steps)
• Sound directions and distances (838 points on 2m sphere)
• Location of the “measurement”point at the entrance of the ear-canal (at the
center of the ear-canal entrance)
• Surface impedances (for skin, hair and torso)

11. Output data
• Head-Related Impulse Responses (HRIRs) used in
binaural renderers (e.g. in SOFA-format)
• Custom output for frequency domain data:
• e.g. Tabulated complex valued pressure for each direction,
distance and frequency

12. Advanced topics
• Ear-canals can be included to the simulation model if the
geometry is available (e.g. using ear-canal scanning, see www.
unitedsciences.com/efit-scanner/ )
• The model can include hearing-aids, headphones, mobile
devices, etc.
• Surface impedances:
• Complex valued as a function of location and frequency
• Other custom simulations

13. Contact information
CEO Antti Vanne
tel +358 50 3566 744
antti.vanne@ownsurround.com
Microkatu 1, FI-70211 Kuopio
Finland