With a soft knee, signals which only just exceed the threshold level are compressed at a low ratio, the ratio increasing the higher the signal level.
Attack sets the time the Compressor takes to respond once the threshold has been exceeded. Attack may be set so that the initial transient of the instrument passes through unaltered, or set to a faster value so that the very start of the sound is compressed. Particularly with drum sounds, careful adjustment of attack time can make the sound more 'punchy' and 'driving'.
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. 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 :
Signal Envelope
Input signal
Fast release
Slow release
Diagram 4
The setting of the correct release time is a compromise. If the release time is too short, background noise can cause effects often known as 'breathing' and 'pumping'. If the release time is too long, the signal will not be compressed, but simply reduced in level. For effective compression, the release time must be set to as short a value as possible before modulation of the background noise becomes too noticeable. The gain reduction bar graph meter will show how much actual compression is going on. If it stays steady, there is little active compression, just a
For a natural unnoticeable compression, attack and release times may be set to Auto. The signal characteristics are continuously monitored for optimum values.
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