This simple compressor circuit controls the dynamics of a speech signal so that loud sounds are controlled to produce a more intelligible voice signal in noisy environments. This is achieved using a novel control mechanism instead of the more usual feedback loop.
 
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This circuit uses dynamic feed-forward compression control rather than the more conventional feedback system which regulates the signal using the output signal level. Instead of a control loop this design uses a method of parallel control and despite its relative simplicity it’s surprisingly effective. An input signal with a dynamic of approximately 50 dB produces a constant output signal level ±3 dB.