Manual-8
COMPressor THRESHOLD, RATIO and GAIN
0
-20
-10
0
-40
-30
+20
+10
dBu
dB
n:1
10
2
1.5
5
-6
+6
1
+12
-12
RATIO
GAIN
COMP THRESHOLD
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0
V
U
Q
V
U
E
#
V
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The threshold, like crossing through a doorway, is the beginning
point of gain adjustment. When the input signal is below the
threshold, a compressor acts like a straight wire. Above threh-
sold, the side-chain asserts itself and turns the volume down.
In Compressor mode,
COMP THRESHOLD
defines the
absolute level, adjustable from –40 dBu to +20 dBu, above which
compression begins. If soft-knee settings are used, the threshold
is defined as the point at the center of the knee. (See the KNEE
description for more details).
In Dynamic EQ mode, this control defines the relative
difference between the broadband program material and the
bandpass signal defined by the PEQ. The
t
pointer between –10
dBu and –20 dBu shows the typical setting for De-essing.
RATIO
defines the ratio of Input change to Output change,
and is adjustable from 1:1 (straight wire, no change) to 10:1
(heavy compression), as shown in Figure 14. For example, a
Ratio of 4:1 means that a 4 dB change at the input causes only a
1 dB change at the output.
The
t
pointer at 10:1 shows the typical setting for De-
essing.
Figure 4. Input versus Output for various Ratio settings (hard knee)
Once you reduce the dynamic range using compression, you
can increase or decrease the overall loudness by adjusting the
GAIN
. This control features a center-detent marking the unity
gain point, with a range of +12 dB or -12 dB on either side.
ATTACK, RELEASE and KNEE
ATTACK
determines how fast the gain is turned down once the
signal exceeds Threshold, and is adjustable from 25 ms (fast) to
500 ms (slow). The
t
pointer at 25 ms shows the typical setting
for De-essing.
RELEASE
determines the rate of gain increase as less gain
reduction is required, and is adjustable from 25 ms (fast) to
2 seconds (slow). It is important to understand the difference
between release
rate
– as determined by this control – and release
time
. The Release setting determines how long it takes for the
gain to change by 10 dB, not how long it takes to return to unity
gain (no gain reduction).
Example
: with the Release control set to 1 s, when a signal
with 5 dB of gain reduction presently applied suddenly drops
below threshold, the release time is 0.5 s, calculated as follows:
Gain Reduction x Release = 5 dB x 1 s = 0.5 s
10 dB 10 dB
Auto Attack and Release
Unsure about how to set the Attack and Release controls? Venue
doors opening in 15 minutes and you need to speed through
sound check? No problem! Simply rotate the Release control
fully clockwise until
Auto
is lit, indicating the Attack and Re-
lease settings are appropriately fixed for most types of program
material. The C4’s not entirely on auto pilot, though – you still
have full control over the Threshold, Ratio, Gain, and Knee set-
tings.
We are the Knights of KNEE
KNEE
controls the action of the compressor above and below
the threshold point. Hard knee does nothing until the signal
exceeds the threshold point, then applies full compression. Soft
knee begins applying a small amount of compression just before
the threshold point is reached, continues increasing compres-
sion through the threshold point and beyond, finally applying
full compression to the highest level signals. Depending on the
application and source material, soft knee settings can sound
more natural. On the other hand for maximum loudness before
compression (for equipment protection for instance), use hard
knee settings.
Knee span is adjustable from 0 dB (Hard) to 10 dB (Soft),
with the Threshold always being at the center of this span. The
t
pointer at the Hard Knee setting shows the typical setting for
De-essing.
ms
ms
500
100
50
250
25
500
125
1 s
2 s
50
25
RELEASE
ATTACK
KNEE
Auto
Auto
Soft
Hard
