Rocktron Intellifex On-Line - Manual (Page 23)

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F. HUSH ® SECTION
HUSH ® is Rocktron’s patented single-ended noise reduction system. The HUSH system contained in the Intellifex Online
is Hush Systems' first fully digital implementation of HUSH achieved through Digital Signal Processing (DSP), and is modeled
after the latest HUSH design.
The low level expander of the HUSH system operates like an electronic volume control. The analog design utilizes a
voltage-controlled amplifier (VCA) circuit which can control the gain between the input and output from unity to 30, 40 or even
50dB of gain reduction. When the input signal is above the user preset threshold point, the VCA circuit is at unity gain. This
means that the amplitude of the output signal will be equal to that of the input signal. As the input signal amplitude drops
below the user preset threshold point, downward expansion begins. At this point the expander operates like an electronic
volume control and gradually begins to decrease the output signal level relative to the input signal level. For example, if the
input signal were to drop below the threshold point by 2dB, the output would drop approximately 3dB. As the input signal
drops further below the threshold point, downward expansion increases. For example, if the input signal dropped 6dB below
the threshold point, the output level would drop by approximately 14dB. A drop in the input level by 20dB would cause the
output level to drop by approximately 54dB (i.e. 34dB of gain reduction). In the absence of any input signal, the expander will
reduce the gain such that the noise floor becomes inaudible.
HUSH PARAMETERS
Hush I/O This parameter simply determines whether the HUSH circuit will be in the
signal path or bypassed.
Exp Thresh The Expander Threshold parameter determines the level at which downward
expansion begins. For example, if the expander threshold was set at -20dB
and the input signal dropped below -20dB, downward expansion would
begin. Typically, this parameter should be set between 5-20dB above the
quiescent noise floor of the input signal (i.e. if the noise floor was -60dB, a
setting between -40 and -55dB will produce the proper expansion).
Rel Rate The Release Rate parameter determines the amount of time required for the
downward expander to decrease the level of the output signal. This rate is
adjustable from 25mS to 800mS to accommodate a wide variety of applica-
tions. For example, when using the expander for gating applications on
drums, a very quick release rate (25-200mS) should be used. When used
with individual instruments such as guitar, a setting of 200mS or higher will
provide adequate expansion without being as harsh as a gate. When used
with sources which have long decay times (cymbals, etc.) a very slow
release rate should be used.