An audio personalisation method for a user, to reproduce an area-based or volumetric sound source, includes the steps of, for a head related transfer function ‘HRTF’ associated with the user, smoothing HRTF coefficients relating to peaks and notches in the HRTF's spectral response, responsive to the size of the area or volume of the sound source; filtering the sound source using the smoothed HRTF for the notional position of the sound source; and outputting the filtered sound source signal for playback to the user.