Lexicon MPX 550 - Manual (Page 33)

Basic Operation
MPX 550
2-5
THE COMPRESSOR
The compressor is available in all programs, except
Dynamics. (Dynamics uses a different compression
mechanism, explained on page 4-33.) The compressor
sits in the wet component of the signal in front of the
effects in the loaded program. It is controlled with four
parameters: CmpRatio, Threshld, CmpAttk, and
CmpRels. These parameters are located on the last Edit
Page for each program, except those in the Cmprssr
Bank.
The ratio (CmpRatio) parameter can be set to ratios of
1:1 (off), 2:1, 3:1, 4:1, 5:1, and 10:1. The threshold
(Threshld) parameter can be set within a 0 to -32dB
range. These settings are relative to 0dBFS (digital
saturation). The compressor is disabled if either the ratio
parameter is set to 1:1 or the threshold parameter is set
high enough to prevent the incoming signal from
crossing the compression threshold.
The attack (CmpAttk) and release (CmpRels) parameters
determine how fast the compressor responds, within
3dB of the output level dictated by the incoming signal.
For most music material, the release time should be
about four times longer than the attack time. Both must
be long enough to accommodate the bass content of the
music.
If the compressor is set to react faster than the waveform
of the music itself, the resulting changes in output level
will re-shape the waveform enough to produce
undesirable audio effects. For example, 80Hz has a
period of 12ms. If this is a dominant component in the
music, set both the attack and release parameters to at
least 12ms, even higher for better results. The
compressor acts on both the left and right channels at
the same time, using the sum of the two channels as its
trigger.
Compression presets are available in the Cmprssr Bank
(see page 4-31). For other compression-only effects,
send compressor output into a Dly/Eko program with
the Delay parameter set to 0. The compressor does not
add propagation delay to the audio path. (Note the
converters introduce about 2ms of propagation delay.)