Noise generators use different noise sources. In the case of thermal noise, the noise of resistors or the noise of active components is used as a noise source. Other noise sources used are current or shot noise, as well as the decay products of radioactive or ionizing noise sources.
The noise signals from noise generators are extremely broadband and are used primarily in measurement technology, but also for random numbers in encryption. In addition, comfort noise is inserted as background noise in digital networks during pauses in speech.