Disclosed is a device which provides a logic signal that indicates a true "on air" event during broadcast production. Each audio channel input from a microphone to a mixing console is coupled to a circuit arrangement which determines whether a mute switch is selected, a fader is set for full attenuation, or an input switch is deselected. If none of these events have occurred a signal is provided to an external display which is optically isolated from the mixing console. This signal controls a tally which indicates to a user that the corresponding input channel, for example, from a microphone is active.