IC1-A is used as a typical non-inverting amplifier. Its gain is equal to 1+[R4/(R3+ rDS)], where rDS is the drain – source resistance of the T1 FET. The FET acts as a voltage controlled resistor (VCR) which is controlled by the voltage potential applied to its gate. IC1-B is a typical inverting amplifier which takes at its input the output signal of IC1-A, and amplifies it furthermore. The gain of the inverting amplifier is defined by the ratio (R10+R11)/R12. D1 and D2 form a rectifier. Together, with C8 and R7, are used as an RMS detector which produces a negative voltage which is roughly approximate to the audio sound level. The time constant C8*(R7+R16) defines the speed of detection, thus also defines the attack and release times of the compressor. The negative voltage which is produced from the RMS detector is applied to the gate of T1 and controls its drain – source resistance, which in turn, controls the gain of the variable-gain amplifier. As the sound level increases, the negative voltage produced by the RMS detector increases. As this negative voltage increases, the drain – source resistance of the T1 also increases and lowers the gain of the variable – gain amplifier. This operation reduces the volume of the loud sounds and compresses the dynamic range of the audio signal. While the time constant C8*(R7+R16) defines the attack and release times of the compressor, the threshold of the limiter is defined by the gain of the non-inverting amplifier which in turn is defined by R11. Thus, R7 can be used to adjust the speed of the compressor and R11 can be used to adjust its threshold.