Rocktron HUSH Pro - Manual (Page 16)

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When used properly, the HUSH Pro should be completely transparent (i.e., it
should not effect the audio signal—only the noise). To maximize the performance of
the HUSH Pro, 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 Pro to suit any application.
The HUSH Pro front panel provides two controls which each manipulate both
channels simultaneously. The HUSH Threshold control sets the amount of noise re-
duction 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 expand-
er.)
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).
Operation