In acoustics and specifically in acoustical engineering, background noise or ambient noise is any sound other than the sound being monitored (primary sound). Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise regulations. See noise criteria for cinema/home cinema applications. Examples of background noises are environmental noises such as waves, traffic noise, alarms, people talking, bioacoustic noise from animals or birds and mechanical noise from devices such as refrigerators or air conditioning, power supplies or motors. The prevention or reduction of background noise is important in the field of active noise control. It is an important consideration with the use of ultrasound (e.g. for medical diagnosis or imaging), sonar and sound reproduction. In astronomy, background noise or cosmic background radiation is electromagnetic radiation from the sky with no discernible source. In information architecture, irrelevant, duplicate or incorrect information may be called background noise. In physics and telecommunication, background signal noise can be detrimental or in some cases beneficial. The study of avoiding, reducing or using signal noise is information theory. In telephony, artificial comfort noise is used as a substitute for natural background noise, to fill in artificial silence created by discontinuous transmission systems using voice activity detection. Background noise can also affect concentration.