Klark Teknik HELIX SYSTEM DN9344 Operator's Manual page 54

If we now replace the parametric with a Helix equaliser and select the dynamic EQ, we have some additional
controls. Frequency and Q controls are as before, but now we have two pairs of controls replacing the single
cut and boost control; these are [low threshold] / [low level], and [high threshold] / [high level]. If we set the
frequency and Q controls to the area that we wish to control, then the processor will monitor the signal level in
that frequency range. If the signal level in this part of the spectrum is below the [low threshold] setting, then
the unit considers this a 'quiet' signal. The EQ applied to the signal will be controlled by the [low level]
control. If the signal level is above the [high threshold] level, then the unit considers this a 'loud' signal, and
will apply the amount of EQ set by the [high level] control. If the signal level is between the two thresholds,
then the equaliser will seamlessly morph between the two equaliser settings in real time. Manual control over
attack and release times is available to set the speed of response to suit the application.
As an example, consider Figure 2, which shows the Helix applying a boost at low signal levels which is
automatically 'wound out'at high level.
igure 2 – Helix with boost at low signal level
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In this example, [low threshold] is -20dBu, [low level] is +12dB, [high threshold] is set to -5dBu, and [high
level] is 0dB. Thus the lowest trace shows an input at -25dBu with a standard parametric boost of +12dB at
1kHz. The -20dBu trace shows an identical response, as expected. However, once above this level, the filter
gradually fades out with increasing signal, until at all levels above 0dBu, the response is flat.
The shape of the curves for -5dBu and -10dBu require some explanation. These appear as they do because of
the nature of the frequency sweep measurement. The Helix equaliser uses a copy of the actual filter in use for
its level calculation, so that depending on the Q of the filter, our input signals are 'ignored' as we move away
from the centre frequency by the correct amount. Thus as the sweep measurement moves across the centre
frequency (1kHz in this case), the dynamic EQ is ramping smoothly in and out again, leading to the curves in
Figure 2. Note that if the level is outside the range specified by the two thresholds, the unit behaves like a fixed
parametric EQ. This means that we do not have to guess how much EQ will eventually be applied - it is
explicitly set in advance.
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