TL Audio 5021 - Manual (Page 14)

4.6 Threshold.
The Threshold is the signal level - measured in dB - above which any
compression comes into operation. The Threshold control is variable from
+20dB in the fully anticlockwise position to -20dB at the fully clockwise
position. Any signal below the Threshold passes through the unit unaffected;
while signals above the Threshold are reduced in gain (and are thus
‘compressed’). This does depend to some extent on whether soft or hard knee
mode is selected, as the soft knee is more gradual in effect around the
Threshold point.
Unlike some compressors, the Threshold control on the 5021 starts at a ‘plus’
value in the anti-clockwise position, and decreases to a ‘minus’ value as you
rotate the control clockwise. The reason for this is as you turn the Threshold
control on the 5021 clockwise (i.e. towards the negative region) then the
degree of compression will increase. We think this is logical, whereas the
common method of turning the control ‘down’ to achieve more compression is
not - but beware, some other compressors may work in the opposite direction!
4.7 Ratio.
Once the input signal has crossed the threshold, the degree of gain reduction
is determined by the Ratio control. The Ratio control is calibrated in decibels
and is simply the change in output level that results from a given change in
input level. An uncompressed signal will have a 1:1 compression ratio - every
1dB change in input level results in the same 1dB change in output level. A
compression ratio of 1:3, for instance, means that a 3dB change in input level
will only give a 1dB change in output level. For more severe compression,
simply turn up the Ratio control.
The 5021 offers a wide range of ratios from 1:1.5 (gentle compression)
through to 1:30 (limiting). Limiting effectively clamps the input signal at the
threshold level no matter how much the signal is increased: this can be useful
when trying to ensure that the signal doesn’t exceed a certain level - for
instance to prevent a digital recorder distorting through overload.
4.8
Attack and Release.
The Attack time sets how quickly the compression is applied once the
threshold has been exceeded, and the Release time sets how quickly the
compression is released (and the signal returns to normal) once the signal
drops back below the threshold. The 5021 Attack and Release controls each
allow a choice of four switched positions between ‘Slow’ and ‘Fast’. For Attack
this covers the range 0.5mS to 40mS, while the Release control spans 40mS
to 4S. There is an element of automatic operation of the Attack and Release
on the 5021: for instance, should a very short transient occur the time