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Apex PE 133 MkII Paragraphic Equaliser (part 2)

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.

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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 situation.

By David Mellor Thursday January 1, 2004
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