ART Pro Audio Tube Channel - Tube Mic Preamp/Compressor/EQ - Manual (Page 11)

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(bypass) position, signal is allowed to pass from the preamp circuitry
to the equalizer circuit with no compression. The LED will glow red
when Bypass is engaged. This informs you that the compressor is
bypassed. In its “out” (Norm) position, the compressor is active.
Use the Bypass switch when setting the compressor’s output level to
achieve unity (no boost or cut) gain. Unity gain is achieved through
the compressor when the active level is the same as the bypassed level.
Toggle the switch between active and bypass while adjusting the
compressor output level. Once the levels are the same (use your ears
and the VU Output Level meter), you’ve reached the unity setting for
the compressor.
Compressor Threshold and Output Controls
The compressor’s Threshold and Output controls are ganged together
on a dual concentric pot. The outer control is the Threshold level and
the inner control is the Output level.
Compressor Threshold Control (outer control)
The Threshold control sets the point at which the compressor circuit
will act on the input signal. Turning this control counterclockwise
lowers the threshold (adding more compression to a signal). Turning
this control clockwise raises the threshold. Setting the Threshold
control is dependent on the Preamp Output control (or the output of
the device plugged into the compressor return insert point). The
easiest way to set the threshold control is to start with the control fully
clockwise. After setting the Preamp Output control, slowly turn the
Threshold control counter-clockwise (lowering threshold) until you see
the yellow (0dB) Threshold LED light in the gain reduction display.
Now adjust the control (either lower or higher) until you have the
amount of compression you desire. Use the Gain Reduction meter as a
visual guide to the amount of compression applied.
Compressor Output Level Control (inner Control)
The Compressor Output level control sets the output level from the
compressor circuit. Typically, the output level of a compressor is used
to add gain to compensate for the amount of compression applied to a
signal. The output level is set to achieve unity gain (no change in level
when compressor is active or bypassed). See Compressor Bypass
Switch for more details on achieving unity gain.