Biomimetic sound-source localization

Abstract

Sound-source localization systems typically comprise free-field microphone arrays. In nature, directional acoustic sensing evolved to rely on diffraction about the head with only two ears. For localization, the brain uses the resultant frequency-dependent acoustic phase and intensity differences between the two ears. We conceive a biomimetic artificial head with microphones placed on its surface. The interaural functions can be computed analytically by modeling the head as a sphere. We define a suitable metric between interaural functions, whose global minimum provides the true source direction. The natural configuration in which the two sensors are placed antipodally on the sphere has intrinsic rotational symmetry: it allows localization only up to a circle around the interaural axis. We describe two methods for breaking the detrimental symmetry in order to achieve full spherical localization capability. First, we consider rotation of the apparatus relative to the source and the information it adds to the localization metric. We derive analytically the gradient of the pressure field under rotation and compute the induced acoustic flow on the interaural localization functions. Second, we explore placing the sensors in configurations differing from antipodal. We show the efficacy of these methods through simulations.