Automatic microphone mixer

Abstract

An automatic microphone mixer for a multi-microphone audio system in which each microphone audio channel is provided with a control channel including a comparator that compares the microphone output, as an A.C. signal, with a D.C. threshold signal, and that switches the microphone channel to 'on' condition when the microphone signal exceeds the threshold; the threshold signal starts at a maximum level for a time T1 and then decreases as a function of time. A D.C. offset is added to the threshold signal in order to prevent low-level extraneous noise sources from activating a channel. All of the control channels are coupled to a threshold signal restoration circuit that drives the threshold signal back to its maximum level each time an audio channel is switched 'on.' An audio channel that has been switched 'on' remains 'on' for a time T2 substantially longer than the time T1. The number of channels currently in 'on' condition is continuously monitored and the output gain is reduced whenever two or more channels are 'on'. The monitoring circuit is also connected to the control channels by a logic circuit and a selector switch. The logic circuit applies control signals to the control channels resulting in all channels either being 'off' in the rest state, one channel being 'on' in the rest state, or two channels being 'on' in the rest state, depending on the setting of the selector switch.