Adventures In Audio
Apex PE 133 MkII Paragraphic Equaliser (part 2)

David Mellor

David Mellor is CEO and Course Director of Audio Masterclass. David has designed courses in audio education and training since 1986 and is the publisher and principal writer of Adventures In Audio.

Thursday January 1, 2004

In theory

We all know the theory behind graphic and parametric EQ so there isn’t
really very much to explain. Or is there? Apex have departed from the conventional
norms and produced a new type of graphic and a new type of parametric. Well,
maybe not totally new, but new to many I would suspect. One thing we do know
about graphic equalisers is that they are the biggest liars apart from politicians
at election time. The curve produced by the sliders on the front panel looks
so much like a frequency response graph that it is almost instinctive to think
that what we see is in fact what we get. In fact, the responses of adjacent
bands interact so that if three adjacent sliders are pushed up to +3dB, then
the response at the centre will actually be somewhere between +6 and +9dB -
rather more than one might expect. Obviously there isn’t any real harm
in this as long as you know what is going on. Also the Q of any individual filter
changes as the setting of the slider is increased or decreased from zero. At
low settings the Q will be low, at higher settings the Q will be higher too.
(Q of course being the sharpness or flatness of the response). Apex have used
a ‘constant Q’ design which, while not necessarily giving a better
or worse subjective result, helps fit the curve produced by the sliders match
the actual audio response.

The parametric section of the PE 133MkII also differs from what you might
expect since the curve produced by each band is distinctly different according
to whether you are boosting or cutting. The boost curve is pretty normal giving
up to +15dB of gain at your chosen centre frequency with a Q of 0.5 to 8. The
cut curve however can go down as far as -45dB , justifying Apex’s ‘non-reciprocal’
terminology. The curves are both, by the way, constant Q so if you set a Q of
1.5, then it stays close to 1.5 no matter how little or how much cut or boost
is applied. It seems strange at first to have an asymmetrical cut and boost
in this way but when you think about it it makes a lot of sense. When you want
to boost, it is usually because you want to enhance a sound or bring out an
instrument from a mixed recording. Would you ever need more than 15dB’s
worth of enhancement? Not often I think. But when you come to use cut, then
as likely as not it’s because you have a problem that you want to get rid
of; hum, dimmer noise or feedback. Anyone who has been involved in PA will know
the dilemma of using EQ to ameliorate the effects of feedback; cut the feedback
and you are also cutting programme frequencies. Particularly if your feedback
is within the predominant vocal range around 2-4kHz then you have to strike
a careful balance. But with a unit such as this, the Q can be set to a high
value and the cut to a great depth so you strike at the heart of the feedback
while only losing a very small proportion of wanted sound. It’s a win-win

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