User Guide
sion without sounding like you’re squashing the daylights out
of the signal. Unlike typical compressors which use VCA’s to
control level detection, the PRO VLA is very musical. The nature
of its operation is much like the way your eye adjusts to light.
Just as your eye transparently adjusts to changes in light, the
PRO VLA adjusts to changes in signal level.
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Your PRO VLA was packed with care at the factory. The ship-
ping carton was designed to protect it during initial shipment.
Please retain this carton for use in transporting the PRO VLA
when it is not installed in a rack, or in the unlikely event that
you need to return your PRO VLA for servicing.
The shipping carton should contain:
- The PRO VLA
- The owner’s manual
- User Registration Card
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The PRO VLA has an internal power supply designed to operate
at 100 to 125VAC, 50 to 60Hz. Units manufactured for use out-
side of the United States of America have been modified to
comply with the required electrical specifications. Under no cir-
cumstances should the power cable be altered. If the cable
becomes cut or damaged,
discontinue its use and have it replaced before operating the
Pro VLA.
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Audio connections to and from the PRO VLA are balanced XLR
(Pin 2 Hot (+), Pin 3 Cold (-), Pin 1 Ground) and active bal-
anced 1/4” TRS (Tip = Hot (+), Ring = Cold (-), Sleeve =
Ground). Unbalanced 1/4” cables may be used with no damage
to the PRO VLA. We recommend using only high-quality cables
equipped with the appropriate connectors.
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The PRO VLA may be employed in a number of setups includ-
ing:
- Between a microphone preamplifier and a mixer, digital multi-
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The PRO VLA (Vactrol-based Leveling Amplifier) is a multi-pur-
pose tool for audio engineering and recording. Enclosed in a
2U (3.5” high) rack-mountable chassis are two independent
channels of analog compression designed to work seamlessly
with any recording, sound-reinforcement, or electronic instru-
ment setup.
A R T’s PRO VLA circuitry is a hybrid design utilizing the latest
and most advanced solid state and tube technology. Using a
transformerless design throughout, the PRO VLA maintains
exceptional signal integrity and extremely low noise. Its VCA-
less design utilizes optical electronics (Vactrol) coupled with a
12AX7 vacuum tube gain stage for superior musical perfor-
mance.
The PRO VLA is a soft knee leveling amplifier by design.
Although it is capable of providing a thoughougly “squashed”
signal, the PRO VLA was designed to excel in areas where trans-
parent, expressively musical dynamics control is desired.
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Compression is used to alter the dynamic range of a signal. In
recording and live sound situations, compression and limiting
is necessary to manage sounds with wide dynamic ranges.
Dynamic Range is measured as the difference between the loud-
est and softest level of a signal. (i.e. from a scream to a whis-
per). Once a signal rises above or falls below the set threshold
(selectable signal level), the compressor automatically changes
its gain to raise or lower the overall signal level. Think of this as
manually moving a fader up and down to try to keep a signal at
a consistent level.
Limiting can be described as a “ceiling”. When using a limiter,
once the signal level reaches the threshold, it is unable to go
any louder - it is limited to a desired level.
In addition to making signal levels more manageable, it is com-
mon practice to apply compression or limiting to a signal to
make it louder or more “in-your-face”. The benefit of using the
PRO VLA for these applications is in its design. By utilizing
opto-electronics, the PRO VLA allows you to add more compres-
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