The present invention relates to systems to attenuate a selected electrical signal in response to changes in selected conditions including changes in characteristics of the signal. Signal attenuation means are utilized in numerous applications from highly sophisticated applications such as computers to more straightforeward applications in simple electrical or electromechanical devices.
Signal attenuation can, of course, be accomplished manually by observation of the situation to be controlled and manual manipulation of the signal control means. In the alternative, signal attenuation can be accomplished by sensing devices responsive to the condition to be controlled and use of controlled devices to automatically attenuate signals in response to changed conditions.
In one application of the foregoing, specifically in electronic circuitry, attenuation can be accomplished by the use of amplifier means for the controlled signal with continuous feedback and gain adjustment of the amplifier circuit. Such arrangements provide satisfactory control in some instances but in other application, for example in attenuation of the output of multiple input sound actuated sound amplification systems, such arrangements have been less satisfactory than desired. Also, such systems are subject to distortion resulting from transient and feedback effects.
Other attenuation methods have provided for stepwise, rather than continuous attenuation. Such arrangements have generally been manually controlled and where automatic control has been provided as disclosed in an article entitled "Automatic Attenuator Rapidly Changes Signal Level", Electronics, Sept. 15, 1969 at page 120 by continuous monitoring of incoming signals to shift attenuation levels. Such systems have been found less than desirable in sound amplification because the rapid switching of output channels leads to undesirable interference with the quality of transmitted program material.
In some sound attenuation devices so called voltage controlled amplifiers have been utilized wherein the attenuation or amplification of a program signal is accomplished by varying the voltage to the gain control of the amplifier to modify the attenuator to maintain selected output signal characteristics. However, such voltage controlled amplifiers have inherently poor noise factors and tend to distort the program to be amplified.