Rear Panel.
The rear panel connectors are identified in fig.3. Make sure that all settings, mains and
audio connections have been made as described above before attempting to operate
the equipment.
OPERATION.
Front Panel.
The front panel controls are identified in fig.2.
Input Gain.
A line level signal should already be at about the correct operating level, but this may
be checked by bypassing the compressor (i.e. turning off the COMP IN switch) and
monitoring the level on the bargraph meter. The INPUT GAIN should be adjusted
until the 0dB LED is illuminated on music of normal loudness, with the red LEDs
illuminating occasionally on higher volume peaks.
The front panel auxiliary input sockets may be switched between high level signals
(“LO GAIN”, suitable for active guitars and keyboards) and low level signals (“HI
GAIN”, suitable for microphones, pick ups or passive guitars), and are also controlled
by the input gain control.
Compressor Operation.
A compressor functions by reducing the gain of the signal when it exceeds a certain
level, or threshold. The amount of gain reduction may be fairly gentle through to
limiting, where the signal is clamped at the threshold level. The amount of gain
reduction is determined by the ratio control, which is calibrated as a ratio of the
output to input signals.
The gain of the signal is reduced by a voltage-controlled circuit. Variable time
constants are applied to the control voltage to adjust the rate at which the gain is
reduced, called the attack time, and the rate at which unity gain is restored after the
signal returns to below the threshold, referred to as the release time.
The effect of compression is to limit the dynamic range of a signal. It may be used to
keep a variable output from a bass guitar, for example, at an even level, or to add
punch to vocals, drums, guitar or a complete mix.
