MOTU Track16 - Desktop Studio FireWire/USB 2.0 Interface - Manual (Page 76)

C U E M I X F X
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mounted so that the emission of the panel
modulates the resistance. An ELP consists of a thin
layer of phosphorescent material sandwiched
between two insulated electrodes to form a
capacitor. Making one of the electrodes
transparent allows the light to escape. These
devices are essentially glow-in-the-dark paint on a
piece of foil covered by metalized glass or plastic,
and are the same devices used in low-power night
lights. Unfortunately, these devices need high
voltages to operate, and are best driven by tube
circuits which can supply voltage swings of several
hundred volts.
Response characteristics
Once the light has faded away, the photoresistor
then decays back to its dark state. The shape of the
decay curve varies depending on how bright the
light was, and how long the light lasted. A general
rule of thumb is that the louder the program, the
slower the release. Typically, the release can take up
to and over one minute. One thing to keep in mind
when using these types of devices is that the typical
concepts of compression ratio, attack, release, and
threshold do not apply. The light intensity is
determined by the highly non-linear interactions
of the input signal, AGC circuit, and ELP, and thus
exhibit a strong program dependence that is
impossible to describe without the mind-numbing
mathematics of statistical mechanics. The actual
results, however, can be almost mystical: even
when you feed the same material (a loop perhaps)
through the Leveler twice, you’ll often see a new
response the second time through a loop, complete
with unique attack times, release times and
compression ratios. Furthermore, two different
input signals with the same RMS levels may be
leveled in a drastically different manner.
It is precisely this self-adjusting behavior that
makes optical compressors the tool of choice for
smoothing out vocals, bass guitar and full-
program mixes without destroying perceived
dynamics.
Compressor/Limit buttons
The Comp and Limit buttons (Figure 9-21) model
the original LA-2A Limit/Compress mode switch.
The effect is very subtle, with the Limit option
behaving only slightly more like a limiter than a
compressor. The switch increases the level of the
input to the AGC model and runs the attenuator at
a slightly lower level. The Leveler then responds
more strongly to transients, but otherwise still
behaves like a leveling amplifier.
Gain Reduction
Gain Reduction (Figure 9-21) sets the strength of
the signal sent to the AGC model.
Makeup Gain
Makeup gain (Figure 9-21) amplifies the output
signal to make up for gain reduction.
Enabling or disabling the Leveler
The Leveler models the LA-2A so closely, it also
models the time it takes for an actual LA-2A to
“warm up” after it is turned on. Therefore, when
you enable the Leveler, give it a moment to “settle”
before you begin processing signals with it.