For determining a subjective property such as loudness of a binaural sound signal left and right sound pressures in the left and right ears of a human being, resulting from the binaural sound signal, are determined. The left and right ear and right sound pressures are frequency analyzed to obtain left and right frequency spectra. In each frequency band, the diotic (common) sound pressure in the left and right ears is determined, which would result from a plane wave frontal incidence on the human being, and that would produce the same perceived loudness as the frequency bandwidth limited left and right sound pressures. In each frequency band the inverse frontal headrelated transfer functions are used to determine the free-field sound pressure that would produce the same perceived loudness as the diotic sound pressure. The loudness is determined as the loudness of the totality of frequency bandwidth limited free field sound pressures, preferably using the international standard ISO 532.