Audio signal compressor

Audio signal compressor is actually an amplifier controlled by its own input signal and having some adjustable level and time parameters. This circuit demonstates the basic principles of dynamic range compression. While the value of input signal (or more precisely the absolute value of its envelope) stands lower some specified threshold value the whole circuit works like an amplifier possibly having voltage amplification coefficient rather close to 1 so it doesnt affect to input signal any magnificent way. Then if input signal becomes greater and exceeds the pre-defined threshold value mentioned above "compession mode switches on" so the circuit changes its own internal gain level which after some time period usually called "attack time" leads to decreasing of output signal compared to the simple amplification mode witout any logic (i.e. having some contant gain level) If it happens so that the input signal becomes lower the threshold value again the circuit gradually recovers after some time called "release time" coming back to the state with the "standart" inital gain level. The given circuit has some auxiliary parts namely relay and indication for sequential switching of the input signal from low (50mV, lower the threshold) to high (200mV, above the threshold) level and vise-versa. Blue plot is an input signal, green is the output one. The orange plot indicates the moments of input signal level changes. Potentiometers from left to right: "Input gain / sensitivity" "Ratio" "Threshold" (at the top of the diagram) "Release time" "Attack time"

published 1 year ago