Patent US 3,944,736

In a video communications system for remotely located conference rooms, a voice-operated switching (VOX) circuit comprising: PA1 1. an audio level discriminator (ALD) circuit for eliminating input audio signals below a predetermined magnitude and for locking out access to the VOX circuit when another VOX circuit is activated; PA1 2. an audio duration control (ADC) circuit for controlling the activation of the VOX circuit and the possible loss of access to and preemption by another conferee during pauses between audio signals from any conferee presently having activated the VOX circuit and associated video system; PA1 3. an attack time control (ATC) circuit for preventing short duration audio signals above the threshold level of the ALD circuit from activating the VOX circuit; and PA1 4. an activation circuit for coordinating the output signals of the ALD, ADC, and ATC circuits and operating a video switcher in response to the aforesaid output signals.