Rocktron HUSH Ultra - Manual (Page 14)

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When used properly, the HUSH Ultra should be completely transparent (i.e., it
should not effect the audio signal—only the noise). To maximize the performance of
the HUSH Ultra, 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 cor-
rectly set up the HUSH Ultra to suit any application.
The HUSH Ultra 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 con-
trol 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 com-
bines 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).
HUSH Description