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Operating Manual - MQX-2310, MQX-1310, and MQX-2150 Graphic Equalizer

7. TYPICAL APPLICATIONS

7.1General Tone Control

The graphic equalizer is a very useful device for

general tone shaping because it is intuitive and easy to

adjust. The visual reference provided by the slider posi-

tion gives an approximate idea of the frequency response

generated, with the lower frequencies on the left and

higher frequencies on the right. To use the power of an

equalizer effectively, you need to translate your idea of

the tone you want to produce into a range of numerical

frequencies. This is simple after a little practise. Here are

a few references which are useful for starting points:

Very low bass (the "wind" in a kick drum,

almost felt as much as heard -40Hz-80Hz.

The low register of a male voice - 200Hz

The low register of a female voice - 350Hz

Lower midrange ("warmth" frequencies) -

400Hz-1KHz

Upper midrange ("harshness", snare drum "bite",

"hot" sound) -2.5KHz-4KHz.

Sibilance ("sss" sounds, cymbal "sizzle") - 8KHz-

15KHz.

Try using these starting points as a guide when

you want more or less of these types of sounds. Adjust

by ear from there. It is always a good idea to remember

that a little equalization usually works out much better

than a lot, and that there are many audio problems which

can not be solved with equalization alone.

7.2 Feedback Control

A graphic equalizer can be used to provide some

control over moderate feedback problems, but does not

have enough flexibility or resolution to handle severe situ-

ations. You will achieve the best results when you can

eliminate one or two feedback points by setting one or

two sliders for no more than a 6dB cut. Often you can

find a feedback point by boosting sliders in succession to

determine which frequency ranges contain the feedback

modes, and then cutting those ranges. Be very careful in

this process to avoid explosive feedback and possible sys-

tem and hearing damage! If you find feedback points

with many equalizer bands, remember that cutting every

band may not help (all you will do is reduce system gain).

The combination of a graphic equalizer for tone control

and a parametric equalizer (such as the Ashly PQX-571

or PQX-572) for feedback control is highly recommended.

7.3 Console Channel Equalization

Many mixing consoles provide only simple equal-

ization for individual channels. If your console has chan-

nel inserts, you can patch your graphic equalizer into a

channel that's being used for something important and

use it to tailor the sound of this channel exactly the way

you want.

7.4 Large Room Equalization

Large rooms tend to suffer from multiple reflec-

tions with long time delays, long reverberation times, and

"ring-modes", all of which lead to reduced intelligibility

and a generally "muddy" sound. As sound travels long

distances through the air, high frequencies are attenuated

more than low frequencies. In general, large rooms ben-

efit from some low frequency roll-off, high frequency

boost, and attenuation of ring mode frequencies. As in

the case of feedback control, a graphic equalizer can help

reduce an isolated ring-mode or two, but a tunable nar-

row-band equalizer such as a parametric is more effec-

tive here.

8. DESIGN THEORY

While most graphic equalizers look very much

the same, there are several important differences in the

circuitry used to implement various designs.

Perhaps the major differences are in the filters.

Some equalizers use a filter made of a capacitor, an in-

ductor, and a resistor, or "RLC" filter. The advantage

here is simplicity, but the real disadvantage is the induc-

tor itself. An inductor is a coil of wire with a core of

some sort. Inductors are susceptible to hum fields and

they are large and expensive.

Other equalizers use the same basic approach, but

replace the inductor with a "simulated inductor", which

is actually a circuit comprised of an amplifier, a capaci-

tor, and a couple of resistors. This adds parts but is less

expensive than a real inductor. The problem with this

approach is that simulation is less than ideal; it produces

an inductor with high resistive loss resulting in poor curve

shape when used in a filter.

Another problem with "RLC" designs is that large

capacitors must be used for the lower frequency filters,

limiting the choice to large, expensive non-polar types or

electrolytic capacitors with poor audio performance. Also,