Often the greatest audio/recording rooms are exposed is the sound from within the building. Noise comes from sources such as lighting, heating, ventilation, equipment used within the studio, mains hum, etc. The other source of noise is the general environment around us, for example, airplanes passing overhead, traffic, emergency services sirens, barking dogs, and automobiles. The only protection from such noise is that offered by the walls, floors, and acoustic of the building.
There are two ways in which sound can be heard: either airborne or impact. It depends upon the person who can hear the sound as to which category it falls into. For example, footsteps would be heard as airborne if the listener is in the same room. If the listener is in the room below, it would be heard as an impact sound. The reason for having to differentiate between the two types of sound is due to different methods of reducing the sound and different types of insulation specific to eliminating certain types of sound.