A disturbance signal which is superimposed on the output signal. It reduces the quality of the output signal and occurs anywhere where signals are amplified, measured or transmitted. Noise arises, for example, in an electrical resistance due to the atomic motion resulting from the influence of temperature or in semiconductors due to the creation and elimination of charge carriers (pair formation and recombination). Noise is classified via the spectral power density, i.e. the power of the noise within an infinitesimally small bandwidth. In engineering noise signals, such as pink noise, are used to assess acoustic components.