dbx 166 - Sidechain Applications Overview

Normally, the
control is set to just under the peak
clipping level of the equipment
downstream.
This
way, clipping will
be softer and controlled
within the 166. The LED
should light occasionally,
on p^ks only? if the LED lights
often, of course, reduce
the
compression threshold and/or
increase the ratio, to
allow less peak signal level at the
output.
SIDECHAIN APPLICATIONS
In
all
the following
situations, it's the Sidechaln Monitor
function that will
save you
time and trouble, letting
you adjust the preceding processor(s)
and instantly confirm
that
things are (or aren't) going
the way you want them to.
General
hints
It's
possible to separate certain vocals and Instruments
from a mix
by
making
the
compressicm frequency-sensitive. With
an equalizer inserted
into the Sidechaln input
(but not in the audio path), the EQ
settings do not shift the timbre
or equalize the audio
signal; they merely alter
the threshold of the compressor
as a function of frequency.
In
such an arrangement, frequencies
that are boosted on
the equalizer will be sup-
pressed in the audio signal. The
converse may also be used, of
course: dipping the equal-
izer on
a
particular
band prevents
any sound with dominant energy in the affected
regis-
ter from compressing
so
much,
because the 166 will detect
less need for compression.
For example, if
you want to suppress an overly loud
bass drum, boost the equal-
izer's response below about 150 Hz. This
will make the compressor reduce
gain whenever
energy in this region is detected. Furthermore,
raising the threshold will
cause this to
happen only on very loud kicks. To put
it generally, a relatively high
threshold setting
can prevent most sounds from
being affected while
solo and very loud sounds within
that
frequency
range are held back. (Of course,
when
compression
does occur, the entire
program level
is affected.) Depending
again on
the
threshold setting, frequencies outside
that range will not
cause compression.
During the recording of cymbals
and toms, a compressor with
an
EQ
in
the
side-
chain path
can help prevent tape
saturation.
The
equalizer can be adjusted for a boost
peaking at about
5
kHz, causing
the cymbal to be compressed on
a
very
loud crash and
stopping saturation of
the tape at higher frequencies,
where there’s less headroom. How-
ever, gentle tapping with
a stick or cymbal brushing will not
be held back. And the tom-
tom likewise, being
a lower-frequency instrument and better-tolerated
by the tape, has
less need for compression.
EQ in the sidechaln circuit
can
make
the compressor not as
readily triggered
by a loud tom-tom beat as by an equally loud cymbal
crash.
De-essing
In the absence of
a
de-esser,
small amounts of high-frequency (6-10
kHz) boost In
the sidechaln path frequently
will help in the processing of
vocals that may have been
brightly equalized beforehand
or that suffer from prominent
sibilance ("ess" sounds).
Speaker protection
If a single compressor
is
to be used with
a
multi-way
sp>eaker system (after EQ,
before
the crossover), you are faced with the problem of keeping the entire system
level
down below the point of destruction of the most sensitive component. If midranges
are
frequently blown, for
example, the whole system must be run at a lower SPL
or addi-
tional mids must
be
added.
By the insertion of an equalizer in the sidechaln of
the
166,
It can be made
sensitive to the frequencies the midranges handle, permitting
the entire
PA system to
be run at higher average levels and dropped back only when damaging
signals are present.
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