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A complete discussion of room acoustics, speaker and microphone placement, and so forth is obviously
way beyond the scope of this manual. Likewise, a perfectly optimized acoustical space with an ideal
sound system is as rare as a humble lead guitarist. Fortunately, the GRAPHI-Q is an ideal tool for
overcoming the shortcomings of the real world. Better sound through electronics is easy and affordable.
So far, the tips offered by this humble narrative are probably familiar to many people purchasing a
GRAPHI-Q. Read on for some less obvious suggestions.
9.2. WIDE AND NARROW FILTERS: GRAPHIC, PARAMETRIC, AND FBX
Here’s a trick question: how wide are the filters in a 1/3 octave graphic equalizer?
The answer to this question is not as obvious as the term “1/3 octave” would suggest. Much confusion
stems from the fact that “1/3” refers to the center points of the frequencies on a graphic equalizer, NOT
the width of the filters. In practice, most audio manufacturers conform to an informal industry norm that
sets graphic EQ filters to a one- octave width.
This means that moving a graphic EQ slider up or down is not
surgically precise, as you are actually controlling a wide band
of frequencies, in a roughly symmetrical “bell curve” pattern
centered on the nominal frequency. And since the width of
each filter (one octave) is greater than the distance between
adjacent graphic EQ center points (1/3 octave), this wide swath
of filters that you’re controlling with one slider actually overlaps
the range of frequencies controlled by sliders to the right and
left. For example, cutting the 1000 Hz EQ slider will also affect
the 800 Hz and 1.25 Hz slider frequencies, to a lesser but still
significant degree.
The diagram at right illustrates the wide cut of a single graphic EQ slider. Is the industry standard choice
of filter width a good or a bad design? It depends entirely on the intended use of the equalizer in question.
There are at least two basic design intentions of equalizers, both of which are designed into the Sabine
GRAPHI-Q:
•
SYSTEM EQUALIZATION. Equalizers are used to achieve a desired system response curve, by
compensating for acoustical resonances of a particular environment, and for the characteristics of
particular audio gear (microphones, amplifiers, speakers, etc.). This kind of EQ is conducive to a
relatively large number of filters of greater width, which facilitates achieving a smooth overall
response. Narrow filter width produces more dramatic peaks and valleys in the response curve.
•
“PINPOINT” EQUALIZATION. Equalizers are also used to correct very specific, relatively narrow-
band problems or deficiencies in audio signals. Common examples would include audio hum induced
by AC electrical current (50 or 60 Hz plus harmonic multiples of those frequencies), or acoustical
feedback that arises when amplified sound is directed back into a microphone or pickup and re-
amplified to the point of screaming oscillation. Using a wide, graphic EQ filter to correct hum or
feedback is overkill, since the filter is much wider than needed and unnecessarily affects frequencies
outside the narrow “problem band.” Using a graphic EQ filter to reduce feedback thus has the
unfortunate side effect of also subtracting a significant portion of the “good audio.” It’s like throwing
the baby out with the bath water.
In contrast to a graphic EQ filter, a PARAMETRIC filter affords a great deal of programmability. All the
“parameters” of a filter can be specified precisely: Filter width, frequency, and dBs of boost or cut. A
parametric filter can be much more “surgically” applied to an audio signal, sometimes with such precision
as to be transparent to the listener, while correcting or improving the signal.
Section Nine: Suggestions for Optimal Use of the GRAPHI-Q