The ITA HRTF-database: A high-resolution head-related transfer function (HRTF) and three-dimensional (3D) ear model database

 

Overview

This database provides HRTF datasets in high spatial resolution with corresponding detailed ear models, reconstructed from MRI-scans, of each individual subject. It contains 48 subjects who are on average 29 ± 5 years old. 35 of the 48 subjects are male and 43 are Europeans, 3 are Asians and 2 are South Americans. For all of the subjects the HRTFs datasets were measured in a resolution of 5° x 5°, and magnetic resonance imaging scans were taken of their head and pinnae.

 

HRTF measurements

Kunstkopfmessungen mit dem HRTF-Bogen ITA

Free-field HRTFs are the transfer paths from one spatial direction to the eardrums of a human subject divided by the transfer paths from the same direction to the center of the head with the head missing.

The measurement setup was designed with the goal to achieve a high resolution and individual HRTF measurement in a very short time period with a low influence on the measurement itself. In order to minimize the influence, the physical dimensions of the setup should be as small as possible. The setup consists of 64 loudspeakers that are placed in the zenith direction with a 2.5 degree distance on a semicircle starting at 1.55° and ending at 160° zenith. The radius of the arc is defined as 1.5 m. The subject is standing on a turntable with the center point of the head as the center point of the arc. The turntable can be adjusted in height to balance out the differences in height of the subjects. For database presented here, the subjects were rotated in 5° steps. Sennheiser KE3 microphones, supported by a dome which blocks the ear, were used to take measurements at the beginning of the ear canal. The measurements were carried out in a semi-anechoic chamber with a stone floor and the head center was set at 2 m above the floor.

The measured impulse responses of one dataset are cropped to a total length of 256 samples which is desirable for real time applications. To suppress angle-dependent notches from the loudspeakers and enhance the SNR of the final HRTFs, the reference transfer functions are regularized.

 
HRTF_horizontalPlane
Video 1
 
 

Ear models

The ear models are determined from the MRI scans of the 48 subjects. The segmentation and geometric reconstruction of the ear geometry was done using different freeware:

 
Ohr ITA
  1. The segmentation of the MRI data was performed with the help of the 3D Slicer software version 4.5.
  2. Afterwards, the surface quality was not sufficient for simulations, as it was rough and contains several holes. Therefore, the mesh was optimized by using the Laplacian mesh smoothing in the MeshLab software version 1.3.3.
  3. With the aid of the GOM Inspect software version 2016, the remaining non-connected surface parts were removed. The other obvious mesh errors were manually corrected by filling the holes.
  4. To minimize the number of polygons, quadric edge decimation in MeshLab was applied. Further occurring mesh errors were corrected by GOM-Inspect.

The final models as depicted in the figure are concerned for the anthropometric dimensions in the following table.

 
 

Table 1: The statistical evaluation of the anthropometric dimensions according to the CIPIC specifications and their percentage errors %.

x1

d1

d2

d3

d4

d5

d6

d7

d9

Mean [mm]

142

18

8

18

19

64

33

5

12

Std [mm]

6

2

2

3

3

5

3

1

4

Min [mm]

123

15

4

12

13

49

27

2

4

Max [mm]

154

23

11

23

26

75

40

8

20

% [ ]

8

22

50

33

32

16

18

40

67

 
Earmodel rotated
Rotating view
 
 

Helpful Software

To display the ear models, the open source software MeshLab or FreeCAD can be used.
The HRTF datasets are optimized for the ITA-Toolbox, an open source MATLAB toolbox http://www.ita-toolbox.org. The SOFA format is specified in the AES standard AES69-2015.

 

Acknowledgments

The project was funded by the German Federal Ministry of Education and Research (BMBF), funding code 01IS14027B. Responsibility for the contents of this publication rests with the authors.

Download HRTF-Database

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Foto von Janina Fels

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