The quietness required for room inside varies according as usage of the room. In case of planning a building, the required performance of sound insulation can be computed from the frequency characteristics of major noise sources outside the building and the quietness required for room inside. Thus it becomes possible to design the specifications of the window sash, the roof and the exterior wall of the building depending on the required performance of sound insulation.
Using digital signal processing technologies, the auralization of transmission sound from outside to inside of a room can be made by playing the recorded sound of an aircraft's flyover through the digital filter designed for the sound insulation. That is to say, it can be possible to listen to the difference of the performance of sound insulation grade (for example, the difference of soundproofing specifications).