BSS Audio FCS-930/960 User Manual v3.0
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This is only likely to occur if the input signal to the unit is quite large and
substantial boost equalisation is being used. In either case the input signal to the
FCS-930/960 needs to be reduced accordingly. Should you be using large amounts
of GAIN then this could also cause the PEAK LED to indicate and suitable
correction can be applied by backing-off the GAIN control accordingly.
8Filter shape and interactive effects
Graphic equalisers have tremendous value in their ability to modify the amplitude
response of a sound system. They have become the most widely used type of
equaliser product for the general sweetening of a sound system, as well as for more
precise work in helping to remove unwanted resonances in a reverberant room or
removing feedback in stage monitoring systems. Their advantages lie with the
visual picture obtained by the fader positions in representing the modifications
made to the frequency response, and with the reciprocal nature of the boost and
cut effect. Their disadvantages lie in having only certain fixed frequencies
available, and with the interaction effect of one fader on its adjacent fader. The
pictorial view of a modified amplitude response as shown by the fader positions is
an ‘idealised’ one. Each filter has a predetermined shape, defined by its Q value
and design topology and the actual result obtained will not necessarily be a
smooth curve, as depicted by the fader knob positions, but rather one which is
defined by the overall shape of each filter and how it combines with its adjacent
filter. For the application of general sweetening where groups of faders will be
moved to form a particular shape, a good combining effect is desired to avoid a
number of humps appearing in the amplitude response. This requires a particular
filter design which is not compatible with that needed when greater selectivity is
required for room tuning and feedback suppression. Moreover, on some graphic
equaliser designs, the Q value will vary as the amount of boost or cut is varied,
further adding to the complication.
On the FCS-930/960 we have carefully optimised the design to account for these
effects. Adding the dual mode feature allows us to re configure the filter shapes to
accommodate the different applications. Using a constant Q filter design removes
the width variation with boost and cut, thus allowing more selectivity at low levels
of boost and cut.
When adjacent filters are adjusted there will always be some interaction affect, and
the degree that is required is dependent on the application.
The FCS-930/960 in its Normal mode shows very smooth combining properties
with almost complete absence of ripple, even at full boost. For the Fine mode
precise selectivity and minimal interaction is achieved at half boost, whilst for full
boost combining ripple is minimal.
