Steinberg HALION4 Mode D'emploi page 180

Dynamics Effects
Expander
Expander reduces the output level in relation to the input level for signals below the
set threshold. This is useful when you want to enhance the dynamic range or reduce
the noise in quiet passages. The graphical control to the left indicates the expansion
curve. You can edit the Threshold and Ratio value with the handles of this control, and
the corresponding knobs reflect your changes. The input and output VU meters
indicate the level before and after the expansion. The Gain Reduction meter indicates
the current attenuation of the level.
Threshold
Use this to set the threshold in dB. Sounds that are softer than the threshold are
reduced in gain. Sounds above the threshold stay untreated.
Ratio
This adjusts the amount of gain reduction for sounds that are softer than the threshold.
The higher the ratio, the more the output is lowered. For example, if the ratio is set to 2:1
and the amplitude of the sound is 4 dB below the threshold, the output is lowered by
2 dB. If the amplitude is 8 dB below the threshold, the output is lowered by 4 dB.
Soft Knee
If this button is off, signals above the threshold are compressed instantly according to
the set ration (hard knee). When Soft Knee is activated, the onset of expansion is
more gradual, producing a less drastic result.
Attack
This determines how fast the Expander reduces the gain when the sound falls below
the set threshold. The longer the Attack time, the longer the period for reducing the
gain will be.
Hold
This sets a time period during which the expansion is applied after the sound falls
below the set threshold.
Release
This determines how fast the Expander raises the gain after the sound exceeds the set
threshold. The longer the Release time, the longer is the period for raising the gain
again.
Auto Release
Activate this to set the Release time automatically. The Expander analyzes the input
sound continuously to find the optimal Release time. The Release knob is disabled
when Auto Release is active.
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Effects Reference