From Electro Harmonix;
A sophisticated noise gate that can tame a single pedal or an entire
effects loop! The Silencers three-control layout provides precise
fine-tuning to fit your system, axe and playing style. Threshold adjusts
how much level is required to open the noise gate and allow a signal to
pass thru. Reduction regulated the degree to which the gated signal is
reduced and is variable between -70dB and +4dB. Release controls how
long the gate remains open after the signal drops below the Threshold.
Release time is variable between 8ms and 4 seconds.

I/O includes inch Input, Output, Send and Return jacks. The
footswitch selects whether The Silencer is engaged or in bypass mode;
buffered bypass allows the effects loop to remain in your signal path
when the gate is bypassed. A built-in AC jack accepts a standard power
supply like the EHX 9.6DC unit (optional) and the pedal comes with a 9V
battery.