Drawmer DL231 Dual Expander/Compressor - Manual (Page 4)

DL231 OPERATORS MANUAL 2
INTRODUCTION
A compressor is a device which automatically controls the level of an incoming signal to
provide a more constant output.
Even in a digital system, which has a large dynamic range, compression is necessary on
some instruments and even on a final mix because the environment in which most
material is heard is often noisy, to say nothing of the limited dynamic range of the
reproduction equipment, e.g. portable radios and cassette players.
A well designed compressor should operate smoothly and create a minimum of distortion
and noise. Such a device in use should go almost un-noticed (unless for special effects)
and require a minimum of adjustment.
A limiter is essentially the same as a compressor but as its name implies, it serves to
prevent the output from rising any higher than a pre-determined level.
The use of compression effectively raises low level signals, but this includes any ambient
noise. For instance, vocals usually require compression, but noise from headphones,
together with the taking of breath, can be a problem for the engineer. This can be
overcome by the use of an expander, which will attenuate signals below a preset level,
i.e. the opposite of compression.
A device which performs which performs all three functions gives all the benefits of
compression and limiting without the unwanted side effects. Additional refinements can
greatly increase the versatility of such a unit by automating some of the more critical
control functions.
The DL231 is a dual channel Expander/ Compressor/Limiter combining ease of operation
with flexible performance. Each channel consists of a compressor, having variable
threshold, ratio, attack, release, and output gain controls; a peak limiter, which is
required to prevent momentary overload when using gentle compression slopes and / or
slow attack times and an expander / gate for the removal of unwanted ambient noise
which would otherwise be ‘pumped up’ by the use of compression.
Although each channel is completely independent, linking is easily accomplished, which
prevents image shifting when treating stereo material.
Particularly attractive features are the unique dual function displays using Tri-colour
LED’s, which measure input signal levels, or gain reduction.
Both expander and compressor release are semi-automatic, programme related and are
adjustable via a single release control thus providing smooth operation and reducing
setting up time.
The expander section is equipped with fully automatic attack, which continuously adjusts
itself to match the rising envelope of the incoming signal. This feature is of enormous
benefit on vocals, because they contain ever changing transient characteristic, which
makes manual adjustment difficult and time consuming, with sometimes doubtful results.
Equalisation may be applied to the compressor side-chain insert points. This allows
frequency conscious compression to be achieved. ‘Side chain listen’ facilities are
provided to allow both side-chains to be monitored.