Rocktron MicroHUSH - Manual (Page 8)

HUSH Information
In most applications, the signal from an instrument being played is much louder than the noise level.
Therefore, much of the noise is not heard when an instrument is being played. However, when
you stop playing or let a note decay, the instrument level drops below the noise level and the noise
becomes much more audible. Setting the THRESHOLD controls just above the level of the noise
causes the MicroHUSH to begin to decrease the output level so that the noise is never heard.
This pedal incorporates the latest advancements in HUSH noise reduction technology. The
MicroHUSH’s discrete threshold control circuit utilizes a voltage-controlled amplifier (VCA) as a
downward expander which can control the gain between the input and output of the MicroHUSH from
unity to over 60dB of gain reduction. When the input signal is above the threshold level set by the
THRESHOLD control, the VCA will remain at unity gain (i.e. the output level will remain equal to the
input level). As the amplitude drops below the threshold point, downward expansion will begin.
When downward expansion begins, the VCA acts like an electronic volume control and gradually
begins decreasing the output signal relative to the input signal. For example, if the input signal were
to drop below the threshold point by 10dB, the output would drop approximately 12dB. As the input
signal drops further below the threshold point, downward expansion increases exponentially. This
means that if the input signal dropped 20dB below the threshold point, the output level would drop
approximately 30dB. A 30dB drop below the threshold would result in a drop of 60dB of the output
signal (30dB of gain reduction). The absence of any input signal will result in the expander reducing
the gain so that the noise floor is inaudible.