Comparison of different playback techniques in binaural head-related transfer function synthesis

In binaural synthesis, the playback device (typically: headphones) can play an important role in achieving the desired perceptual authenticity. One potential source of error is the variability of headphone transfer functions when the headphones need to be taken off and on again after equalization. To avoid this issue, Erbes et al. (2012) proposed a device with miniature loudspeakers located about 5 cm away from the ears, which could remain in place. However, the device itself forms an obstacle not present in normal listening conditions and may therefore introduce direction-dependent artifacts. As an alternative, we propose a device which is placed in the subjects' ear canals. Due to its small size and the position in the ear canal, it is hoped that artifacts will be independent of the direction of sound incidence. In order to compare the two devices which remain in place to the more traditional playback over classical headphones, binaural syntheses were generated for 432 source positions (12 elevations and 36 azimuths) and related to transfer functions from real sources to microphones of a dummy head with ear canals. It was found that the agreement between synthesis and measurement was best with the in-ear device.