DL241 OPERATORS’ MANUAL
2
INTRODUCTION
The DL241 is a dual channel compressor/limiter designed to fulfil the needs of
professional studio and live sound applications. It may be used in balanced or
unbalanced systems and each channel is independently switchable b4dBu and
-10dBu operating levels. In addition to the compressor/limiter, each channel also
contains an independent expander and peak limiter.
In order to maximise flexibility while simplifying set up and operation, several new design
concepts have been incorporated. The compressor section combines aspects of both
the traditional ratio style compressor and the soft-knee approach, making it equally
adept at creative work and unobtrusive level control. The control layout resembles that
of a straight ratio style unit but the transition from unity gain to gain reduction at the
selected ratio is progressive and occurs over a nominal 10dB input level range.
Traditionally, soft-knee compressors have been preferable for unobtrusive level control
where the original sound is to be changed as little as possible, whereas ratio type
compressors are generally considered more successful in creative applications or where
large amounts of gain reduction are required. By combining these two elements, the
DL241 is capable of outstanding results in a very wide range of studio and live sound
situations.
One of the perennial problems in using compression is that maximum system gain
occurs during extremely quiet passages or during pauses which results in an increase
in background noise, the degree depending on the amount of compression being used.
The accepted way of dealing with this problem is to include in the compressor, a
separate expander section with its own threshold control so that a low level gating action
may be applied to keep pauses clean. But the problem with simple expanders is that,
even when properly set up, they may unwittingly process low level sounds as they have
no means of identifying them from noise. On a vocal track, for example, this can lead
to the starts or endings of words being accidentally removed, especially if the singer has
a wide dynamic range.
The DL241 uses an entirely new Programme Adaptive expander circuit which varies its
ratio depending on the dynamics of the signal being processed. Because the onset of
expansion is progressive, those low level signals most at risk will be treated to a lower
ratio of expansion while the residual noise during pauses will be subjected to a higher
expansion ratio and will, in consequence, be attenuated more. The outcome is an
expander that requires less stringent setting up and is more tolerant of wanted sounds
that are only slightly above the residual noise floor.
A further feature of the DL241 is a peak limiter which allows the user to set an absolute
output signal level that will not be exceeded. If the peak limiter threshold is exceeded
for more than a few milliseconds, additional gain reduction will be applied to reduce the
overall signal level to within accepted limits without distortion. Once the peak has
passed, the system gain will return to normal over the period of about one second. This
facility is extremely valuable both in live sound applications, for driver protection, and
in digital recording where an absolute maximum recording level exists. Furthermore,
when overdriven, it can be used creatively to produce deliberate level pumping effects.
