Consoles 895expected of an inductor and capacitor combination—a
slope of 12 dB/octave as opposed to a single-order
effect of 6 dB/octave. Fig. 25-73 shows what it does as
an EQ element.
The response is hinged about 1 kHz. The control
varies the frequency (between 5 kHz and 20 kHz) at
which the gain reaches maximum (or minimum if the
boost-and-cut control is cut). The slope between 1 kHz
and the chosen maximum frequency is virtually a straight
line representing a nearly constant dB/octave character-
istic, with a nearly flat-top shelving characteristic.
In electronic terms, this is achieved by progressively
degenerating the supercapacitor until it’s no longer
super—i.e., it eventually ends up looking like a simple,
single capacitor.25.12 DynamicsDynamics processing is becoming as common in
today’s signal paths as equalization. Many commercial
mixing consoles carry dynamics as standard on a
per-channel basis. Formerly, the occasional necessity of
hanging in external dynamics processing was the major
justification for channel insert (or patch) points. These
patch points were typically either before or after (pre- or
post-) equalizer in the signal chain as shown in Fig.
25-74.
Preequalization actually amounts to postinput stage;
the purpose of an insert point here is to control unruly
input signals that may otherwise clip later in the
chain—in particular within the EQ section where
serious amounts of gain at some frequencies may be
instituted. Characteristically this pick-off point is after
any high-pass filtering, so that any low frequency
rumble that may cause false triggering within the
dynamics may be removed. On the other hand, the
post-EQ insert point allows control over the entire
channel immediately prior to the channel fader and is
commonly used for automatic gain controlling.
Dynamics is automatic control of signal level by an
amount determined by the characteristics of the signal
itself. In a linear 1:1 circuit, what goes in comes out
untouched and unhindered. For example, if we have a
circuit that automatically senses the input signal and
uses that measurement to control the output signal, if
the input signal rises in level by 6 dB, the output signal
is controlled to rise only 3 dB. The output signal has
been compressed by a ratio of 2:1 with respect to the
input signal.
There are four basic types of dynamic signal
processing:
- Limiting.
- Gating.
- Compression.
- Expansion.
It is arguable that limiting is a special case of
compression and that gating is similarly a special case
of expansion, effectively reducing the number of basic
groups to two. Although in practice the means of
achieving these pairs of effects are indeed similar, true
definitive compression is a long way from limiting, as
gating is from expansion. The discussion about time
constants etc. within the following Limiting section is
directly applicable to each of the other sorts of
dynamics.
Fig. 25-75 shows a now customary style of
input-output signal level plot of a compound (more than
one dynamics type active) dynamics section, with
typical slopes for each of limiting, compression, and
expansion. (Measured plots of actual dynamics sections
can be seen also in the discussion of digital dynamics
later.) This style of dynamics display is common on
programmable consoles; here it can be a handy form of
visualization or representation as the various types are
discussed. Linear (i.e., no processing) is represented by
the dotted line, showing equal output for input. Unusu-
ally (!) a section of linear remains in this compound
curve, displaced upward by 15 dB; this is a normal
occurrence when automatic gain reduction such as
compression and/or limiting is used. In order to make
up for the gain reduction above the threshold, some gain
is applied to compensate and bring the output signal
back up to usable levels. This is often called makeup, or
buildout gain.25.12.1 LimitingThis is the conceptually easiest and most commonly
applied form of dynamics processing. Nearly any audio
heard outside of a recording studio has been passed
through a limiter at some point in the chain—TV audio,
radio, even (and especially) CDs. This very pervasive-
ness has had the rather odd unforeseen effect that cultur-
ally we have gone beyond acceptance and become
dependent on the sound of excessive limiting and heavy
compression; even to educated ears a new CD can
sound wrong or wimpy in comparison to what had been
heard on the radio, where typically murderous addi-
tional processing is applied. Record shops actually do
get complaints like that. The race to be louder than loud
has unfortunately spilled over into the record production
arena back from radio where it had previously raged