User guide

PreComp™ Preamp and VCA Compressor
True to the Music
®
Radial Engineering Ltd.
6
Gain: As you increase the amount of compression by lowering the threshold or raising the
ratio, the dynamic range is reduced and less output is produced. The compressor gain control
is used to compensate for this and is sometimes called a ‘make-up’ gain because it replaces
the gain lost in compression. Simply adjust the gain control to bring the output level back to
where it was before adding compression. Try comparing the pre and post compressed effect
by using the in/out switch.
+10dB -
0dB -
-10dB -
+10dB -
0dB -
-10dB -
+10dB -
0dB -
-10dB -
Before compression: signal is
over threshold.
After compression: dynamic
range is reduced.
Output gain compensates for
reduced dynamic range.
Fast/Slow: The compressor’s attack and release settings are automatically adjusted in real
time based on the dynamics of the input signal. The FAST/SLOW switch allows you to choose
how the compressor responds to the input signal. When set to slow, the compressor will allow
the initial transient to pass before the compression effect kicks in. This is often used with
singers for a natural vocal sound with smooth dynamics.
SLOW AT TACK FAST ATTACK RESULT
Setting the speed control to fast will cause compression to occur the instant the signal goes
over the threshold. A fast setting is often used with percussion to make sure the initial transient
does not cause digital clipping at the recorder. Set the speed control to suit.
Soft/Hard-Knee: For the most part, there are two fundamental compression curves known as
hard-knee and soft-knee. The knee is the pivot point where compression begins. Hard-knee
compression abruptly affects transients above the threshold while soft-knee sets in before the
threshold and does so in a smoother fashion.
The PreComp dynamically adjusts the compression curve from soft-knee to hard-knee based
on the incoming program material. At lower levels the compressor automatically uses a soft-
knee curve for a natural rendering but as peaks are encountered and dynamics increase,
the compression curve pivots toward a hard-
knee curve ensuring the output stays within the
predetermined range. In the chart to the right
the soft-knee curve is represented by the long
dashed line, the hard-knee by the short dashed
line. You can see how the soft-knee applies
gradual compression as the signal approaches
the threshold while the hard-knee curve reduces
the gain once the signal has gone above the
threshold.
+10dB
0dB
-10dB
-20dB
-30dB
THRESHOLD
SOFT
HARD
-40dB
-50dB