Abstract: An apparatus and method removes repetitive background noise from an information signal originating from a first source, such as a microphone. The noise originates from a second source, such as a siren, and is picked up by the first source along with the information. The noise signal has a characteristic frequency and associated period. The information signal is delayed for a selected period of time based on the characteristic frequency of the repetitive noise signal and forms a phase-shifted or delayed information signal. The delayed information signal is processed with a substantially non-delayed information signal and forms a processed information signal in which the information component is substantial and the noise component is negligible.