Compressor/Limiter Section (Operation)
By measuring the dynamic range of musical instruments in live recording situations, you will find that extreme amplitudes will
occur which can lead to overload in subsequent signal processing equipment. In most application, these signal peaks can lead to
heavy distortion. To avoid this kind of distortion or, for example, to prevent loudspeakers from being damaged by overload,
compressors or limiters are used. These devices use automatic gain control to reduce the amplitude of loud passages and
therefore restrict the original dynamics to a desired range. This application is particularly useful in microphone recording to
compensate for level changes caused by varying microphone distances. Although compressors and limiters perform similar
tasks, there is one essential difference. Limiters abruptly limit the signal above a certain level while compressors control the
signal “gently” over a wider range. A limiter continuously monitors the signal and intervenes as soon as an adjustable threshold
level is exceeded. Any signal exceeding this threshold will be immediately reduced back to the adjusted threshold level. A
compressor also monitors the program continuously and has a certain threshold level. However, in contrast to the limiter, signals
exceeding the threshold are not reduced abruptly, but gradually. Above the threshold, the signal is reduced in level relative to
the amount the signal exceeds this point. Generally, threshold levels for compressors are set below the normal operating level to
allow for the upper dynamics to be musically compressed. For limiters, the threshold level is set above the normal operating level
in order to provide reliable signal limiting and thus protect subsequent equipment.
The extensive controls of the Compressor section provide a great range of dynamic effects: from musical and soft compression to
limiting signal peaks, right up to extreme and effective compression of the overall dynamics. For example, a low ratio and very
low threshold setting can be used to achieve soft and musical processing of the general dynamics of the program material.
Higher ratios, together with low threshold settings, create relatively constant volume (leveling) for instruments by preventing the
output level from significantly exceeding the threshold point (provided the OUTPUT controls in the 0 dB position). Please note
that the compression of the entire program material (achieved by low threshold settings) sounds less natural with higher ratio
settings. Ratio settings in the range of 4:1 and lower affect the dynamics of the program material less and are often used to
compress the sound of a bass guitar, a snare drum or a vocal. Sensitive and moderate settings are generally used in mixing and
for leveling of program material in broadcasting.
In the CL-5000, control of the dynamics process is achieved by means of a high quality VCA (Voltage Controlled Amplifier) with
an operating range of about 60 dB, i.e., the input signal level can be reduced or increased within a range of 60 dB. Input signal
levels below the adjusted threshold are not reduced. However, as soon as the input signal exceeds the threshold level, dynamics
control is activated. The amount of compression (gain reduction) is proportional to the amount by which the input signal exceeds
the threshold level. With the threshold control completely turned clockwise, the threshold value is +20 dB. Since such a value will
not be reached in practice, you can use it to disable the compressor section and work exclusively either the expander/gate and
the dynamic enhancer circuits.
Rotate the THRESHOLD control counterclockwise until an appropriate amount of gain reduction is indicated on the GAIN
REDUCTION meter. This operation will be accompanied by an audible drop in output level. The OUTPUT control should now be
turned clockwise to reinstate the output level. Final adjustments of the controls can then be made to suit your particular require-
ments, including the RATIO, ATTACK and RELEASE controls. The AUTO function of the attack and release times provides pro-
gram dependent dynamic processing, which suits most standard uses. If a “condensed” or “wider” sound processing technique
is required, the attack and release times can also be manually adjusted.
The experienced user will be in a position to specify parameters while in bypass mode and thus realize the effect before the unit
is actually switched into operation. This is important in live situations, where a signal needs to be managed efficiently by the
sound technician, without the convenience of continuous A/B comparison. For using the Compressor/Limiter as a Limiter, you
should set Ratio turned fully clockwise to
∞
:1, switch out the AUTO function and manually adjust short Attack and maximum
Release times. Use the THRESHOLD control to set the threshold for the limiting level.
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