A method of estimating an individualized head-related transfer function (HRTF) and an individualized interaural time difference function (ITDF) of a particular person, comprising the steps of: a) obtaining a plurality of data sets (Li, Ri, Oi), each comprising a left and a right audio sample (Li, Ri) from a pair of in-ear microphones, and orientation information (Oi) from an orientation unit, measured in a test-arrangement whereby an acoustic test signal is rendered via a loudspeaker; b) storing the data sets in a memory; c) estimating the directions of the loudspeaker relative to the person based on the orientation data and the audio data; d) estimating the ITDF based on the data sets and on the estimated relative position/orientation; e) estimating the HRTF, based on the data sets and based on the estimated relative position/orientation.