Rane DC 24 Users Guide [RaneNote 130] - Manual (Page 2)

DC 24 Users Guide-2
DYNAMICS 101: A PRIMER
Let’s start with what a dynamic controller actually does.
No matter how you cut it, these are electronic volume
controls. It is a hand on a control, 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.
SIGNAL CHAIN
Conceptually, dynamic controllers have two internal paths,
the signal and the side chains. The signal chain is the path the
main signal takes through the unit: through the input circuits,
the gain control device and then through the output circuits.
The signal chain goes through the “volume control” in the
“hand on a control” analogy.
SIDE CHAIN
The side chain is the hand which turns the control. Side
chain circuitry examines the input signal and issues a control
voltage to adjust the amplification of the signal. There are a
number of parameters governing side chain activity, but the
four most commonly discussed are threshold, ratio (or slope),
attack time and release time. Some dynamic controllers offer
adjustment of each of these parameters, while others have one
or more preset at an optimum setting for the application.
THRESHOLD
The threshold, like crossing through a doorway, is the
point at which gain adjustment begins. When the input signal
is below the threshold, a dynamic controller should be like a
straight wire. Above, the side chain asserts itself and turns the
volume down.
RATIO
Once the threshold is exceeded, just how far the volume
goes down depends on the ratio (or slope) setting. An
ordinary preamp or a straight wire has a ratio of 1:1, that is,
the output level tracks the input level perfectly. A 2dB change
at the input produces a 2dB change at the output. A severe
ratio is perhaps 8:1 or 10:1. For a 10:1 ratio, a 10 dB blast at
the input would rise only 1 dB at the output – heavy compres-
sion. Kinder, gentler ratios are in the 2:1 to 3:1 range.
ATTACK TIME
Attack time is the time which passes between the moment
the input signal exceeds the threshold and the moment that
the gain is actually reduced. Attack times generally range
between 1ms and 30ms.
RELEASE TIME
Release time is the time which passes between the rnoment
the input signal drops below the threshold and the moment
that the gain is restored. Typical release times are between .1
seconds and 4 seconds.
Some of the oldest compressors were called levelers, which
are becoming popular again.They had very slow attack times
and very long release times to provide volume adjustment of
overall program level for broadcast. If you shouted repeat-
edly, the level would slowly fall off for about 30 seconds,
then it would take another minute or so to recover.
COMPRESSORS
A compressor, when the input signal reaches the level set
by the Threshold control, begins turning down the signal by
an amount set by the Ratio control. Most modern compressors
make the loud signals quieter, but do not make the quiet parts
louder. (However, by keeping the loud signals under control,
you can turn up the output level which will make the quiet
parts louder along with the rest of the signal.) Some compres-
sor designs actually do raise quiet signals below the thresh-
old. These designs might be called “upward expanders”.
LIMITERS
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 is allowed
through. A limiter has a relatively high threshold, very fast
attack and release times and a very high ratio, approaching
infinity:1.
EXPANDERS
An expander is a compressor running in reverse. Above the
threshold, a compressor reduces the gain; below the threshold
an expander reduces the gain. A compressor keeps the loud
parts from getting too loud, an expander makes the quiet parts
quieter.
GATES
A gate is an expander with the ratio turned up. With the
proper settings (low threshold and a high ratio), a gate can be
applied to remove noise between louder sounds, and is often
called a noise gate for the way it can lock out background
noise.
GATE / EXPANDERS
A low ratio acts as an expander that turns quieter signals
down, while a high ratio acts as a gate that shuts signals off.
SIDE CHAIN EXTRA #1: SEND/RETURN
The gain control voltage is derived from the side chain
audio. If you were to put a signal with treble boost into the
side chain audio, it would not effect the treble in the main
signal path, but it would cause the high frequencies to cross
the threshold sooner or more often. Large peaks of treble
could be set to cause heavy compression with virtually no
compression at other times. What we’ve just designed here is
the basic de-esser, a circuit to remove excess sibilance. With a
bass boost you can make a de-thumper and with a midrange
boost a de-nasaler. Most compressors have a send and return
available in a side chain loop to patch in an equalizer for
these purposes.
SIDE CHAIN EXTRA #2: SLAVE
Many compressors and expanders make the side chain
control voltage available to connect to a neighboring unit, or
to tie internal channels together. This is called slaving or
linking the compressors, and it causes the units to compress