Noise is interference of an electrical or acoustical nature; more generally, any unwanted, bothersome, or distracting sound. Random noise is a desirable signal used in acoustical measurements. Pink noise is random noise whose spectrum falls at 3 dB per octave: it is useful for use with sound analyzers with constant percentage bandwidths.
Background noise is the noise which, In the absence of a signal, comprises all interference, including hum and hiss, in a system which stores, reproduces, or measures sound. Its level is measured by the signal-to-noise ratio. The term is also used colloquially to denote ambience.