Rocktron Prophesy II - Manual (Page 24)

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HUSH
®
Page
HUSH ® is Rocktron's patented single-ended noise reduction system, and is avail-
able in all presets. The HUSH system provided in the Prophesy is a fully digital imple-
mentation, modeled after the latest analog HUSH design, achieved through Digital
Signal Processing (DSP).
How HUSH ® works
The low level expander of the HUSH system operates like an electronic volume con-
trol. The analog version of the
HUSH
system utilizes a voltage-controlled amplifier (VCA)
circuit which can control the gain between the input and the output from unity gain to 30,
40 or even 50dB of gain reduction. When the input signal is above the user-set threshold
point, the VCA circuit remains 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 level drops below the
user preset threshold point, downward expansion will begin. It is at this point that the
expander acts like an electronic volume control, gradually decreasing the output signal
level relative to the input signal level. As the input signal drops further below the threshold
point, downward expansion increases (see figure below). A drop in the input level by
20dB would cause the output level to drop approximately 40dB (i.e., 20dB of gain reduc-
tion). In the absence of any input signal, the expander will reduce the gain so that the
noise floor becomes inaudible.
The
HUSH
circuit is located after the A/D converter in the signal chain to reduce any
noise generated from the guitar and the A/D converter. This ensures a quiet input signal to
the preamp section. Because the preamp section of the Prophesy is digital, it is virtually
noise-free (even in the high-gain mode). Therefore, a quiet input signal to the preamp will
result in a quiet output signal.