PreSonus CL44 - Manual (Page 8)

The ratio selected for the compressor determines the amount of activity of the expander on the incoming signal.
Attack
Attack sets the speed at which the compressor 'acts' on the input signal. A slow attack time (fully clockwise) allows the
beginning envelope of a signal (commonly referred to as the initial transient) to pass through the compressor
uncompressed, whereas a fast attack time (fully counter-clockwise) subjects the signal to the ratio and threshold settings of
the compressor more rapidly.
The Attack control is only active when the Auto button is not pushed in. When the auto button is pushed in, the compressor
automatically determines the appropriate attack time for compression.
Release
Release sets the length of time the compressor takes to return the gain reduction back to zero (no gain reduction). Very
short release times can produce a very choppy or 'jittery' sound, especially in low frequency instruments such as a bass
guitar. Very long release times can result in an over compressed sound, sometimes referred to as 'squashing' the sound. All
ranges of release can be useful at different times. You should experiment to become familiar with the different sound
possibilities. (Refer to the applications section of this manual for some ideas.)
The Release control is only active when the Auto button is not pushed in. When the auto button is pushed in, the
compressor automatically determines the appropriate release time for compression.
Limiter
The limiter on the CL44 has a fixed compression rate of greater than 20 to 1, and a fast fixed attack and release. The limiter
knob allows you to set the threshold level.
Optical
Engaging the Optical mode applies a DSP emulation of an optical transfer curve to the signal. This transfer curve provides
the desirable audio qualities derived by using vintage optical limiters. Optical mode is especially effective for adding warmth
and presence to a signal. Adjacent channels are link-able allowing the operator of the CL44 the option of having a stereo
optical limiter for use on “mix-down” which would provide a very pleasant analog quality to the signal. Vocal performances
can benefit significantly from the pleasing quality provided by the emulation of the transfer curve of an optical limiter.
Auto
When pushed in, the auto button places the compressor in automatic attack and release mode. The attack and release
knobs become inoperative and a pre-programmed, input dependent attack and release curve is used.
Gain
Compressing a signal usually results in an overall reduction of output level. The gain control allows you to restore the loss in
output level due to the activity of the compressor on the signal. (Like readjusting the volume.)
2.3 BYPASS & LINK