The damping characteristics of the materials it is made out of are important in noise absorption. The wetness or moisture level in a medium can also reflect sound waves, significantly reducing and distorting the sound traveling through it, making moisture an important factor in soundproofing. Distance- the use of distance to dissipate sound is straightforward. The energy density of sound waves decreases as they spread out, so that increasing the distance between the receiver and source results in a progressively lesser intensity of sound at the receiver. In a normal three dimensional setting, the intensity of sound waves will be attenuated according to the inverse square of the distance from the source. Damping is the process by which sonic vibrations are converted into heat over time and distance. This can be achieved in several ways. One way is to add a layer of material such as lead or neoprene which is both heavy and soft. These can be used as a sound deadening layer in such areas as wall, floor and ceiling construction in sound studios where levels of air borne and mechanically produced sound are targeted for reduction or virtual elimination. Lead and neoprene do not address the lower, most bothersome low frequency vibrations and can be very difficult to install as well as costly. A room within a room (rwar) is one method of isolating sound and stopping it from transmitting to the outside world where it may be undesirable. Noise cancellation generators for active noise control are a relatively modern innovation. A microphone is used to pick up the sound that is then analyzed by a computer; then, sound waves with opposite polarity (180° phase at all frequencies) are output through a speaker, causing destructive interference and cancelling much of the noise.