XTA DPA SERIES, Руководство оператора, Страница: 67 / 78

DPA Series — DPA80/DPA100 Operating Instructions Page 67
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Peak Limiter
The main limitation with traditional dynamics control is the inability of the processing to react
truly instantaneously to the signal. One of the most significant advantages of digital signal
processing over analogue is the ability to delay the audio signal precisely and without
extensive complex hardware. The entire domain of digital signal processing is based around
the combination of delaying, multiplying, and accumulating numbers (representing samples
of audio) to implement all the filters and dynamics processing we have come to expect today.
In the case of dynamics processing, being able to delay a signal allows the processor module
to delay the main signal in relation to the sidechain (the signal being monitored relative to the
threshold), so that it can compensate for peaks prior to the arrival of the main signal.
Consider the situation of a monitor engineer listening to a band perform. Having no access to
dynamics processors, he has had to resort to manually ‘riding the faders’ in an attempt to
keep control of the levels. Should the level of one of the channels on his desk reach an
unacceptably high level, he will turn it down appropriately.
There is a hidden sidechain in
operation even in this case.
The main signal path is fed
through the monitor desk and
the gain controlled by
adjusting the fader. The
sidechain is formed by the
feedback path between the
engineer’s ears checking the
level and his brain instructing
his hand to turn the fader
down if the volume goes over
the threshold he has chosen.
In this case, the delay between the signal actually going over the threshold, the engineer
registering the situation, and then turning the signal down will be in the order of several
hundred milliseconds at best. This will only be true if he is not distracted — in reality, it may
be several seconds before any gain reduction is imposed on the signal to bring it under
control.


Audio Input
(Signal being
monitored)
Gain Control
Element
Output to
Amp/Speaker
System
Feedback Path from Monitor Engineer’s Ears to Hand
forming Sidechain Control Signal