Ashly LIMITER/COMPRESSORS CL-100 - Manual (Page 5)

been reached. For veiy fast transients, such as hand claps, snare drums, or
other percussive soimds, a very fast attack time is usually desirable so that
the limiter can respond in time to control the peak level. On other types of
program material, a slower attack time may be preferred. A too-fast attack
may, on some material, “square ofiT the top of a waveform, produtíng a
distorted sound. The Ashly CL Series provides continuously variable attack
times finom 200 microseconds to 20 milliseconds.
Release Time
Another parameter which affects oompressordimiter performance is
Release time, or the time required for the limiter to restore system gain to
nonnal after the input agnal has fallen below threshold level. Again, proper
Release tíme will depend on the type of program material being processed
and the way in which the limiter is being used.
When subtle limiting is desired, slow release times are often chosen to
avoid a condition referred to as “pumping” or “breathing”. This occurs when
overall gain is modulated up and down by repeated peaks which are followed
by quieter intervals. If the release time is set too fast, then the overall level
will jump up and down, producing an objectionable and unsettling effect.
Note that, in some cases, an individual track or channel which seems to be
pumping may sound acceptable when heard in context of a complete mix.
A unique feature of the Ashly Compressor/Liiniters is the incorporation
of a double release-time constant. When a conventional compressor/limiter is
adjusted for slow release times, transients such as mic “pops” and record
scratches may cause a severe reduction in gain followed by a slow fade-up,
making the action of the limiter very obvious. Wi\h the double time constant,
release from gain reduction after a brief transient is always fast, with a
slower release after a sustained overdrive.
Output Leve/
Because compression and limiting are both gain reduction processes,
the output of a oompression^limiter is frequently at a lower level than the
nominal system level. To make up for this loss, an OUTPUT level control is
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provided to restore up to 18 dB of system gain, NOTE: When the unit is in
the BYPASS mode the OUTPUT control still functions.
Bypass Switch
This switch enables you to quickly switch the CL compressor/limiter in
or out of the audio chain, making comparisons between processed and
unprocessed signals easy. When the switch is in the OUT position, all
limiting and compression controls and fimctions are bypassed, with the
exception of the output control, which continues to function as a
straightforward level control. For all normal compress and limit functions,
this switch should be depressed to the IN position.
Threshoid/Gain Reduction Indicators
Five LED’s on the CL-50E and CL-100 front panels provide a convenient
visual indication of the amount of gain reduction that is taking place at any
time. As soon as the OdBV threshold level is reached, the yellow LED
illuminates. Depending on how far the input level rises above threshold, and
the settii^ of the RATIO, ATTACK, and RELEASE controls, successive red
LED’s will illuminate, indicating increasing gain reduction.
Gain reduction is a useful way of expressing compressor/limiter action.
We have seen that Ihe increase in output level of a compressor/limiter is less
than the increase in input level by some amount. Using a limit ratio, output
level will remain nearly constant as input levels increase above threshold.
Wth a gentle ratio, say 21 , input signals above threshold will be “gain-
reduced” at the output by exactly 1 / 2 . Ihus, gain reduction can be expressed
as input level increase divided by output level increase. For example, a +12
dBV input signal that is 3:1 compressed will produce 4 dB of change at the
output, and 8 dB of gain reduction has occurred (12 d£ input minus 4 dB
output = 8 dB gain reduction). The -6 dB red LED on the CL-50E or CL-100
front panel would be seen to lii^it up because we are past 6 dB reduction, but
not jet to lOdB. □
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