Rocktron HUSH The Pedal - Manual (Page 7)

The Variable Integrated Release (V.I.R.) technology contained in
each HUSH circuit automatically adjusts the release rate of the expander
based on the dynamic decay rate of the incoming signal. If the input
signal stops suddenly, downward expansion will occur rapidly (similar to
a gate). If the input signal decays slowly, expansion will occur slowly
without disrupting the dynamic decay of the input signal.
The THRESHOLD control should be adjusted by listening to the
noise floor while not playing. Turn the THRESHOLD control clockwise
to the point where the noise floor becomes inaudible. Turning too far
past this point will cause the downward expander to attenuate the output
level too quickly and not allow the signal to decay as long as it should.