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Chapter 6: Compressor Control Functions
DN540
20 Operator Manual
Release time plays a very important role in compression. During periods of high signal
level, gain is reduced. When the signal level falls below the threshold, the gain will
increase at a rate determined by the RELEASE control knob. If the release time is
short, the gain will rise quickly. A long release time will mean that the gain will stay at
its reduced level, only recovering gradually, see Figure 2 “Compression fast and slow
release signal envelope graphs”.
The setting of the correct release time is a compromise. If it is too short, background
noise can cause effects such as breathing and pumping. A release time that is too long
results in a signal that is not compressed, but merely reduced in level. For effective
compression the release time must be set as short as possible before modulation of the
background noise becomes too noticeable. The ATTEN gain reduction meter will show
how much actual compression is occurring. If it is steady, there is little active
compression, just a steady-state reduction in level. The faster the meter level moves
up and down, the harder the compressor is working.
Ratio
Ratio is the strength of compression above the threshold level and controls the amount
of compression applied to signals that are over threshold. Ratio is expressed as a ratio
of signal level changes from input to output. For example, when the compressor is set
to 2:1, every 2dB input level change will only generate a 1dB output level change,
assuming the signal levels are over threshold. The highest ratios are achieved when
the ratio control is fully anti-clockwise.
Note: Although the RATIO control knob on the DN540 operates in the opposite way to
more conventional units, that is, the ratio is increased by turning it anti-clockwise
rather than clockwise, we feel this is better ergonomically. This is because turning the
control anti-clockwise results in less output, which matches the threshold and make up
gain.
Figure 3: Compression ratio graphs of 2:1 and 12:1
As can be seen from the graphs in Figure 3 “Compression ratio graphs of 2:1 and 12:1”,
the higher the ratio, the greater the effect.
At a compression ratio of up to 2:1, the effect is mild and suitable for the subtle
compression of vocals or of a complete mix. At 3:1, compression is becoming stronger
and more noticeable. Ratios between 3:1 and 5:1 are suitable for the compressor
sound, which is used as an effect in its own right. Higher ratios are used for the control
of extremely peaky signals.
Input level (dB)
Output level (dB)
+20
+10
-10
-20
2:1
+10 +20-10-20
Input level (dB)
Output level (dB)
+20
+10
-10
-20
12:1
+10 +20-10-20