Abstract: A noise reduction system for removing unwanted audio noise during a pause. The system receives an intelligence plus noise signal that is split and fed to a first rectifier having a first polarity, and through a filter to a second rectifier having a polarity opposite to the first rectifier. The filter removes components below a frequency where most energy-frequency is distributed in human speech. The output of the rectifiers is summed to produce an output signal when most audio noise between pauses in voice is reduced.

Abstract: A noise reduction system and method for reducing noise occurring during pauses in information bearing audio signals has an audio input connected to one input of a differential output circuit. A variable gain circuit has an input connected to the audio input and an output connected to the other input of the differential circuit. A dc control signal is derived from the incoming signals and controls the variable gain circuit to cause cancellation of a noise only signal during periods of no information bearing audio signals.

Abstract: A selective wave filter that employs a frequency selective circuit that provides a waveform that represents the envelope of an input tone burst, such as a dot or dash used in radio telegraphy. The output of the frequency selective circuit is connected to a rectifier and the output of the rectifier is connected to a filter that removes most of the audio components and allows the resultant pulse to pass to an output circuit. The output circuit employs apparatus in the form of a balanced modulator, voltage controlled amplifier or the like.