Spatial cue reproduction in modern receiver-in-the-ear hearing instruments

This study investigates the ability to preserve spatial cues in receiver-in-the- ear (RIE) instruments for six different hearing aid manufacturers. In this particular study, the instruments were fitted bilaterally assuming a symmetric hearing loss profile. In cases where the manufacturer recommended a specific programming option to maximize spatial awareness, this option was chosen. Otherwise, the default mode was applied. S2 and N4 audiograms were used to mimic hearing-loss and testing was performed in an anechoic chamber on a KEMAR head. In order to mimic the peripheral filtering of the auditory system the left and right signals were filtered using a gammatone-filterbank. ILD's were estimated at the output of each band across angles from 0-360 degrees and compared to the corresponding values of the open-ear-response. ITDs were determined by low-pass filtering the left and right input signals and using a cross- correlation technique in order to find their respective time shift. Distortions of ILDs were as large as 10 – 15 dB for certain manufacturers whereas ITD distortions lay between 20-100 μs.