Nilfisk Alto BK 2.0 Benutzerhandbuch

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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.

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 BK 2.0 the attack time can be set in a range of 
1 to 200 milliseconds.

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

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 BK 2.0 can be set from 0.05 to 4 seconds.

This switch turns off the possibility of manually set the attack and release times. An intelligent program recognition 
circuit will automatically set the attack and release times. In such way, undesirable effects such as distortion and 
pumping will be avoided.

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

This switch simply turns off the correspondent channel. This is useful to compare quickly the processed and 
unprocessed signal.