Manual-4
OPERATING INSTRUCTIONS
A PRIMER
Let’s start with what a compressor actually does. No
matter how you cut it, this is an automatic volume control. It
is a hand on a knob, turning the volume down and turning it
up again. The hand is really quick and really accurate, but it’s
just turning a volume control.
When the input signal reaches a level set by the THRESH-
OLD control, the compressor begins turning down the signal
by an amount determined by the RATIO control. The MC 22,
like most compressors, operates by making the loud signals
quieter, but does not make the quiet parts louder. However,
by keeping the loud signals under control, the entire system
may be turned up when necessary to make the quiet parts
louder.
PRE-FLIGHT CHECKLIST
Before proceeding, it’s a good idea to turn the control
knobs to the following positions:
1. LEVEL control ....................... 0 dB
2. THRESHOLD control .......... fully clockwise
3. RATIO control ....................... fully counterclockwise
4. COMPRESSOR switches .. ACTIVE (out)
This renders the MC 22 with no compression, but allows
signal through at unity gain. No change occurs either in the
ACTIVE or BYPASS position of the COMPRESSOR switch.
LEVEL
Before making any Threshold adjustments, set the LEVEL
control so the +4 dBu LED lights occasionally, and the OL
LED does not light. Be aware that changes to the Input Level
will affect the Threshold level.
THRESHOLD
The threshold is the point at which gain adjustment
begins.
When the input signal is below the threshold, the MC
22 acts like a straight wire. When the signal is loud enough to
cross the Threshold, the compressor is active and turns the
volume down. Various Threshold points are illustrated in
Figure 1 below. How
much
it gets turned down is determined
by the RATIO control (shown at 2:1).
RATIO
Once the threshold is exceeded, the increase in output
compared to the input signal increase depends on the RATIO
setting. An ordinary preamp set for unity gain or a straight
wire has a ratio of 1:1, that is, the output level tracks the input
level perfectly. A 2 dB change at the input produces a 2 dB
change at the output.
For a 10:1 ratio, a 10 dB blast at the input would rise only
1 dB at the output –
heavy
compression. Kinder, gentler ratios
are in the 2:1 to 3:1 range. Figure 2 illustrates various Ratios.
Figure 1. Set to 2:1 Ratio. Thresholds at -40 dBu, -20 dBu, and 0 dBu.
Vertical axis = output level, horizontal axis = input level.
FIgure 2. Threshold at -20 dBu. Ratios of 1:1, 2:1, 4:1, and 10:1.
Vertical axis = output level, horizontal axis = input level.
Referring to Figure 2, note that the Ratio indicated is the
average over 40 dB of compression. The ratio is initially
lower. This action provides a “soft” response which is less
audible than hard limiting. For example, the 10:1 ratio
response shows an initial ratio of about 6:1 and ends with a
ratio of
∞
:1.
ATTACK TIME
Attack is the time which passes between the moment the
input signal exceeds the threshold, and the moment that the
gain is actually reduced. This can be a difficult control to set,
so Rane made it easier by pre-setting an attack time of 30 ms/
10 dB step, an optimal setting for a wide variety of material.
RELEASE TIME
Release time is the time which passes between the
moment the input signal drops below the threshold and the
moment that the gain is restored. Another difficult control for
the average user to adjust, Rane presets the release rate at
0.3 dB/ms.
LIMITING
A limiter is a special form of compressor set up especially
to reduce peaks for overload protection. In other words, it is
a compressor with a maximum ratio. A compressor is usually
set up to change the dynamics for purposes of aesthetics,
intelligibility, or recording or broadcast limitations. Once the
threshold of a limiter is reached, no more signal increase is
allowed. The MC 22 acts as a limiter when set at a very high
ratio of 10:1.
0 dBu
-20 dBu
-40 dBu
1:1
2:1
4:1
10:1