For an analogue dynamics
processor, the situation is much
better. Controlling the gain
electronically, and not relying on
a human sidechain feedback
mechanism, it can react much
more quickly.
The red waveform represents the
input to the dynamics module,
with the dotted line showing the
threshold for gain control to
occur. There are several peaks
towards the start of this signal
that are above the threshold, and
so the dynamics processing
should react to these as
appropriate. (In this case reduce
the gain).
The blue waveform shows the
output of the dynamics module.
The circled peak demonstrates that the processor has missed the first peak above the
threshold (as it is very fast and short), but has ‘caught up’ shortly afterwards, keeping all
other peaks under control. As it is unable to predict what is coming, this will always be a
failing with analogue dynamics processing.
The peak limiter pre-delays the sidechain signal, resulting in a “zero overshoot” limiter,
which is able to catch all peaks and provide a reliable absolute maximum setting for the
output of any channel.
The pre-delayed sidechain is
shown in green, with the main
signal in red. As the main signal
arrives slightly after the
sidechain, the output from the
unit does not suffer from the
overshoot problem.
Remember that this delay is only
in the order of tens of
microseconds,and is a pre-delay
— the sidechain is moved back in
time in relation to the main
signal. Inserting a delay into the
main signal path of an analogue
dynamics processor will achieve
similar results, but with the
penalty of delaying the main
signal by the amount of look
ahead delay introduced.
Level
Time
Time
Threshold for Onset of Gain Control
Overshoot here as dynamics processor cannot
predict or react fast enough to this peak.
Input of module
Output of module
Level
Time
Time
Threshold for Onset of Gain Control
No overshoot as sidechain was able to react
before the main signal arrived, due to predelay
Input of module
Output of module
Predelayed sidechain signal
Main signal arrives slightly later
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