Inter-Laboratory Round Robin HRTF Measurement Comparison

Head-Related Transfer Function (HRTF) measurements underlie the signal processing used in binaural auditory displays, but measurement techniques, equipment, and postprocessing vary substantially between laboratories. This variation can result in significant differences in measured spectral and timing data taken from the same subject for the same sound source locations. An ongoing project for comparing databases from laboratories across the world (colloquially titled “Club Fritz”) employs a single dummy head microphone for measurements (Neumann KU-100) at various sites. The current study examines magnitude and timing differences between left and right ear data from 12 different HRTF sets taken from 10 different laboratories. Results revealed spectral magnitude variations up to 12.5 dB for frequency bands below 6 kHz and up to 23 dB above that, as well as large spectral left/right asymmetries (dcorr 0.4) for high frequency content. Further subjective studies are necessary to determine the perceptual relevance of these findings. 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.