Rocktron HUSH Super C - Manual (Page 10)

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When used properly, the HUSH ® Super C should be completely
transparent (i.e., it should not effect the guitar signal—only the noise). To
maximize the performance of the Super C, it is necessary to understand its
front panel controls and how they work together. By understanding how
these controls work, it will be easier to correctly set up the Super C to suit
any application.
The Super C front panel provides two controls which each manipulate
both channels simultaneously. The HUSH Threshold control sets the amount
of noise reduction required for a given input signal, while the Gate Threshold
control provides additional downward expansion when increased. (The Gate
Threshold control may also be used by itself, allowing the unit to be used as
strictly a downward expander.)
HUSH ® Section
Rocktron's patented HUSH ® noise reduction is a single-ended system
that combines the principles of dynamic filtering and low-level downward
expansion.
Dynamic Filtering
Dynamic filtering is achieved by dynamically-controlling a low pass filter
to open and close the bandwidth of the output signal depending upon the
amount of mid and high band information present in the input signal. The
filter bandwidth will only open far enough to pass the highest frequency
information in the input signal, thus reducing the noise above it.
For example, if the highest frequency present in the input signal is
8kHz, the filter will open to pass up to 8kHz while the noise from 8kHz to
20kHz would be reduced. If a signal with frequency components up to 20kHz
appears at the input, the dynamic filter will open to its full extreme (40kHz).
Operation