The outer ear, the pinna, shapes the incoming sound wave, giving cues for sound source localization. The microphones of \textit{behind the ear} type hearing aid are placed behind the ear resulting in no natural shaping of the sound by the pinna, which, in turn, robs the hearing aid users of important spatial cues.

The main focus of the thesis is investigation of the transfer function from the hearing aid microphones to the ear canal. These measurements will be the base of the pinna reconstruction transfer function (PRTF) which is to restore the pinna cues for hearing aid users. A measurement setup were made which allowed for obtaining head-related transfer functions from 611 unique sound source positions in a sphere around the four subject who participated. From these measurements pinna reconstruction filters were synthesized. The PRTFs shows a great change in their directivity patterns as a function of elevation when compares to those of a delay-and-sum beamformer. Additionally, a real-time test platform was to be developed on which hearing aid signal processing can be performed in order to evaluate localization performance of the pinna reconstruction filters and compare it to a delay-and-sum beamformer. The real-time simulation platform was tested by performing dynamic binaural synthesis.