Noise is universal and multi-faceted. In everyday life, the aspects we encounter tend to be annoying, for example, loud conversations when we wish to enjoy a quiet cup of tea, or students chatting during a lecture. But acoustic noise can sometimes be useful e.g. when it indicates that the kettle is boiling, as an essential prelude to the tea, or when it helps to awaken somnolent students at the end of the lecture thereby eliminating the mutual embarrassment of needing to awaken them.