Graphic Equalizers - PRESONUS STUDIOLIVE 24.4.2 Owner's Manual

Owner's Manual

Graphic Equalizers

5.3
EQ-O-Matic
The StudioLive 24.4.2 features 4 stereo (split mono) 31-band 1/3 octave
graphic EQ that can be inserted on the Main output bus, the Subgroups,
or any of the Auxes. When the GEQ button is enabled, the meters and
encoders of the Fat Channel become the controls for the Graphic EQ. As
you touch a knob, you will notice that its band number, frequency and gain
are displayed in the System Menu. The 31 bands range from 20Hz to 20
kHz. If these were analog graphic equalizers, each would look like this:
menu, the meters will flip. You will notice that all meters have one LED illuminated
to display the current gain position for each band, the meter for the selected
band in the Show Band field is inverted, meaning that all LEDs will be illuminated
except the LED displaying the current gain position for that band. The band does
not have to be selected in the Show Band field for its encoder to be active. All
encoders are active so you can make changes to 24 of the 31 bands at one time.
The StudioLive Graphic EQ features an innovative design that sets it
apart from traditional graphic EQs. Traditionally, a 31-band graphic EQ
uses 31 second order shelving filters with fixed frequencies in order to
simulate a curve set by the user via 31 front panel sliders. A well designed
graphic EQ creates an output frequency responses that corresponds as
closely as possible to the curve displayed graphically by the sliders.
In an analog EQ, this is achieved by carefully choosing the bandwidth of the filter
and deciding how or if it varies with the gain and how the filters are summed
or cascaded. In general, narrower bandwidth signifies a higher quality EQ. But
in traditional graphic EQ designs, the center frequency of each band is fixed.
PreSonus took a different approach with the StudioLive. The StudioLive Graphic
EQ is a pool of shelving filters from which coefficients like cutoff frequency,
bandwidth, and gain are extracted through a process of curve fitting. The curve
entered by the user is first oversampled. The system then works with an internal
curve made up of 128 bands to find coefficients for the first shelving filter
that, when subtracted from the user's curve, will produce the flattest possible
response: 0 dB. The resulting response is then used to find coefficients for the
second shelving filter through the same optimization process. Coefficients
for all available shelving filters are found through a recursive process.
Unlike conventional designs, the frequency and bandwidth of the "bands"
depends on the curve entered by the user. This allows for much tighter matching
of that curve. Because of this innovative design, the accuracy of the StudioLive
EQ might feel "wrong" at first. The curve fitting process is capable of very steep
transitions and, unlike conventional analog graphic EQs, what you see is what
you get. With a carefully drawn, smooth curve the StudioLive EQ will have almost
no frequency ripple. The StudioLive EQ is also capable of very sharp notches.
To widen a notch or a bump on a particular band, just bring the adjacent bands
closer to that band's gain and the bandwidth will change accordingly.
Scene, Presets, and the System Menu
Graphic Equalizers 5.3
The frequency for each band
is fixed. Bands 5-28 are
controlled by encoders 1-24
respectively. When Band
4 or 29 is selected in the
Show Band field in the GEQ
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