The present invention is directed to creating sound reverberation. In accordance with a preferred embodiment, an apparatus estimates an impulse response for use in reproduction of a sound in a desired acoustic space. In particular, the apparatus collects space information concerning an acoustic space and point information indicating positions of a sound generation and reception points in the acoustic space, estimates a set of acoustic ray paths of the sound traveling from the sound generation point to the sound reception point, acquires directivity information indicating an acoustic directivity of the sound generation point and the sound reception point, estimates an acoustic intensity of each acoustic ray path and weights each acoustic intensity by the acquired directivity information, and determines the impulse response based on directions of the respective acoustic ray paths toward the sound reception point and the weighed acoustic intensities of the respective acoustic ray paths.