Abstract: A switched capacitor integrator is used within the feedback loop of an automatic gain control (AGC) circuit to provide a very long time constant (5 minutes or more) when the amplitude of the gain-controlled signal is within predetermined limits. The time constant is automatically and quickly changed to a much shorter value when the gain-controlled signal is outside the predetermined limits, thereby allowing the AGC circuit to rapidly bring the gain-controlled signal amplitude within the desired range between the predetermined limits. Time constants of orders of magnitude longer than those readily realized with prior art methods of long time-constant filtering are achieved.

Abstract: A noise trap circuit particularly suitable for use in an electro-acoustic system, operates to suppress low level signals or noise while allowing a relatively large signal to pass unattenuated between input and output terminals of the circuit. Blocking elements between the input and output terminals establish a high impedance path to the noise but switch to a conductive state when the large signals are present at the input terminals. Shunt elements across the output terminals provide a low resistance path or "crowbar" when only the noise is present at the input terminals, but switch to a non-conductive state when the large signals are sensed at the circuit input.