Coloration perception depending on sound direction

Coloration is a phenomenon in which timbre changes when reflected and direct sounds are mixed. We studied the relationship between the perception of coloration and direction for two sounds. Our psychological experiments using 11 subjects suggested that a 50% threshold of coloration appears to have no difference depending on direction. When the level ratio of two sounds is closer to 0 dB, a difference appears: If direct sound comes from a lateral direction and reflected sound comes from the opposite direction, coloration perception does not increase monotonically even if the ratio approaches 0 dB. We assumed that the difference depending on direction resulted from the directional dependence of the spectrum including the head-related transfer function (HRTF) and proposed a numerical model for predicting psychological results using the comb structure on the spectrum observed at the eardrum. We measured spectra using a head and torso simulator (HATS) and calculated the area, eventually finding a quantitative relationship between the area and psychological results and proposing a prediction model based on this relationship.