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4.2.2 Ratio control
This control sets the change of input level to output level but only for the signals that exceed the threshold.
The scale of the ratio control on the front panel (calibrated in dB) indicates how much input level is required
to increase the output level by 1 dB. If you have a ratio equal to 1:1 you will get the same level of input and
output signal: So, no level change.
If you have a ratio of 2:1 this means that for every 2dB increase of the input level (above threshold) you will
get an increase of output level of 1 dB. ON the same way, a ratio of 10:1 means that for every 10 dB increase
of the input level (above threshold) you will get an increase in output level equal to 1dB, and so on.
You need to be aware that higher ratio settings produce less natural sounds so if you wish a more minute
effect on the dynamic range of a program you should use a Ratio of 4:1 or lower.
With the SKC circuit (Smart Knee Control) you can avoid aggressive compression generated by using high
ratios. How we achieve this? Introducing a "soft knee" curve in the range of up to 10dB above the threshold
level. Hard Knee compression is then used beyond this range.
Output
Hard Knee
Threshold
Gain 0 dB
Ratio 2:1
Ratio 4:1
Limiter :1
SKC Curve
Input
Chart. 5 SKC characteristic of the compressor section
4.2.3 Attack control
The attack time represents the amount of time that passes before the compressor start to lower the output
level when the signal is above the threshold point.
For very fast transients such as drums, handclaps, etc, a short attack time will be used. These peaks are
consequently carefully regulated by the compressor. Sounds of other nature will get advantages if longer
attack times are used. Anyway, our advice is always to begin the process with longer attack times. Then you
can start gradually to reduce the attack time. IN the ACL2 PRO the attack time can be set in a range of 1 to
150 milliseconds.
4.2.4 Release Control
This control determines how much time the compressor needs to get back to normal gain when the audio
signal falls below the set threshold.
A too short release time will make the volume to fluctuate and you will experience pumping effect. A too long
release time will give you pumping and breathing effect especially when you have loud passage followed by
a quite passage. The release time on ACL2 PRO can be set from 0.05 to 5 seconds.
4.2.5 Auto switch
This switch turns off the possibility of manually set the attack and release times. An intelligent program re-
cognition circuit will automatically set the attack and release times. In such way, undesirable effects such
as distortion and pumping will be avoided.
4.2.6 Output control
This Control is indispensable to compensate the loss of level at output level generated by the gain reduction
caused by the compression and limiting processing.
4.2.7 Bypass Switch
This switch simply turns off the correspondent channel. This is useful to compare quickly the processed
and unprocessed signal.