# A Review on Head-Related Transfer Function Generation for Spatial Audio
## Appendix A  
This appendix presents an overview of the publicly available HRTF databases. Table A1 summarises the discussed databases, providing key information regarding the number of measurement points \(N\), the range of considered elevations, azimuth, distance, the type of sound source, and the measurement method used for HRIR acquisitions. For measurements taken from human subjects, the number of subjects, and the type of microphone are reported. For measurements performed with mannequins, the type of head and torso (HAT) simulator is provided. The database MIT-KEMAR (1994) [41] is obtained using a [PERSON] mannequin placed at a distance of 1.4 m from a Realistic Optimus Pro 7 loudspeaker inside the MIT anechoic chamber. A total number of measurement points of 710 is provided, considering the elevations from \(-40^{\circ}\) to \(90^{\circ}\), with a step of \(10^{\circ}\), and azimuth from \(0^{\circ}\) to \(360^{\circ}\), with variable steps \(\geq 5^{\circ}\). The impulse responses have a length of 512 samples and are measured using maximum-length pseudo-random binary sequences (MLS) and a sampling frequency of 44.1 kHz. The database CIPIC (2001) [147] is a subset of the HRTFs of more than 90 subjects measured at the CIPIC Interface Laboratory. The publicly available dataset consists of 43 real subjects and the Kemar mannequin with large and small pinnae, resulting in a total of 45 subjects. The dataset includes the impulse responses with a length of 200 samples for 1250 directions and anthropometric measurements. A total of 64 Bose Acoustimass loudspeakers were uniformly mounted along the hoop at 1 m to the subject to consider the elevations sampled in \(360/64=5.625^{\circ}\) steps from \(-45^{\circ}\) to \(230.625^{\circ}\). The azimuth angles were sampled non-uniformly considering steps \(\geq 5^{\circ}\). For real subjects measurements, Etymotic Research ER-7C probe microphones were used. The impulse responses were calculated with a sampling frequency of 44.1 kHz using Golay-code signals. Anthropometric measurements are also contained in the dataset. The LISTEN database (2003) [221] consists of 187 locations per subject and 51 subjects. The HRIRs, 512 samples long, were measured at different azimuth resolutions for 10 respective elevation angles spaced at \(15^{\circ}\) from \(-45^{\circ}\) to \(90^{\circ}\) with a sampling frequency of 44.1 kHz. A Tannoy system 600 loudspeaker was installed at a distance of 1.95 m and Knowles FG3329 microphones were used for the acquisitions using logarithmic sweep signals. The PKU&IOA database (2009) [222] was created by using the Kemar mannequin and a spark gap type BDMS1-040528 as the sound source. The signal generated by the spark gap was about 0.5 ms, corresponding to a length of 32 samples with a sample rate of 65,536 Hz. The elevations were sampled from \(-40^{\circ}\) to \(90^{\circ}\) with a \(10^{\circ}\) increment and a full \(360^{\circ}\) azimuth loop was considered, resulting in 793 locations, repeated for eight different distances, i.e., 20, 30, 40, 50, 75, 100, 130, and 160 cm, for a total of 6344 positions. The FIU database (2010) [223] consists of individual HRTFs of 15 different subjects considering 6 elevations, i.e., \(-36^{\circ}\), \(-18^{\circ}\), \(-0^{\circ}\), \(18^{\circ}\), \(38^{\circ}\), and \(54^{\circ}\), and \(12\) azimuths spaced of \(30^{\circ}\) from \(-150^{\circ}\) to \(180^{\circ}\), resulting in 72 HRIRs for each subject with a length of 256 samples, acquired with a sample rate of 96 kHz using Golay codes. The measurements were carried out using the AUSIM3D HeadZap system, specifically designed for HRTF acquisitions in reflective environments. Anthropometric measurements of the various parts of the pinna are included in the database. The SYMARE database (2013) [224] provides HRIRs of 61 subjects for 393 directions, including elevations from \(-40^{\circ}\) to \(90^{\circ}\) and azimuth from \(0^{\circ}\) to \(360^{\circ}\) with a resolution of \(10^{\circ}\).