VTCL-2 Tube Optical Compressor User’s Guide
CONTROLS
Input Gain: sets the input level that goes into the gain stage amplifier of the compressor/limiter. This level should
be set just below the level that causes the overload LED to light for the best signal to noise ratio. (Occasional
blinking of the LED is OK.)
Threshold: turned to the left, or maximum setting, no compression will take place. Turning the control to the
right (clockwise) lowers the threshold and compression will begin to take place. The amount of change in ampli
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tude you hear can be seen if you set your meter selector to change. Turning up the output gain control compen
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sates for the volume loss.
Attack: sets the speed at which compression takes place. This control has a great effect on the sound and
because of its range (0.5 milliseconds to 200 milliseconds) it can be set to realize a broad range of sounds and
effects. For most applications the attack control should be set to the fastest speed (fully clockwise) where the
attack is inaudible.
Release: sets the time the signal remains compressed after the input signal drops below the threshold level. This
control has a wide range (200 milliseconds to 10 seconds) and can best be set by ear to achieve the most natu
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ral sound. Please note that the greater the amount of compression used the longer the release time will be.
Meter Range Switch: this switch sets the sensitivity of the meter to either normal (0 db) or to higher sensitiv
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ity (-10 db) for use with semiprofessional equipment.
Meter Selector Switch: selects which information the meter is showing. Set on Input the selector shows the
unaffected signal coming in. Output shows the signal level going out.
Change: shows the amount of change in level as the signal is being compressed.
Output Gain: sets the output level of the compressor limiter. This control is used to match levels after compres
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sion has taken place.
Bypass Switch: selects between the affected signal and the input signal and routes them though the unity gain
tube output section. This control is useful in hearing how much the signal is being effected. In the out mode the
compressor/limiter can be used as a tube buffer to warm up the audio signal path.
Mode Switch: selects between dual mono and linked stereo. In the dual mono mode the compressor/limiter
is two separate units. In the stereo mode the input signals are mixed to activate the compressor circuit. The
threshold, attack and release on channel one control both channels together. Input, output and meter controls
are still separate.
Ratio: although the unit has no ratio control the ratio is affected by the amount of compression used. From 0 dB
to 6 dB of compression the ratio is 4 to 1 (that is, if the input voltage increases 4 volts the output will increase
1 volt). From 6 dB to 10 dB the ratio is 6 to 1. From 10 dB on the unit acts as a limiter with a ratio greater than
20 to 1. This input sensitive ratio gives the compressor its natural sound.
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