Graphic Equalizers

We will now analyze the use of graphic equalizers. These are equiped with slide controls that work on a specific frequency decided by the manufacturer. The number of slides and therefore the number of frequencies varies from model to model. As an example we will use an equalizer with 10 bands (frequencies), and therefore 10 slide controls. Now suppose you want "lower" the body of the sound from 200hz to 2Khz (1Khz = 1,000hz): the procedure is very simple, in that all you need to do is lower the slides of the desired bands.

Adding more bass and treble is done like this:

We have obtained the classical "V" equalization, which is often used for distorted rhythmics.
The intervention of a graphic equalizer increases the further the slide is from its central position. Not all graphic equalizers have the same appearance. For instance programmable midi's have rack effects equiped with a small display for the equalizer. These are adjusted using button or knob controls. It is important to remember that the graphic equalizers workable frequencies are fixed (those noted below each slide). If for example you want to accent the 70hz but only have controls of 20, 50, and 100hz, you have to be satisfied with the closest available frequency, which is 50hz. When you adjust a frequency using a graphic equalizer, in reality you are slightly and gradually manipulating the near frequencies.
Lets look at an example: increase the 5Khz to 15db.

The graph clearly illustrates that both the 2Khz and the 10Khz have inevitably increased to about 3db. This situation is called bell, Q or Bandwidth and can only be adjusted with parametric equalizers. With graphic EQ's it is fixed and therefore cannot be changed. The exaggerated use of the graphic equalizer in all the bandwidths will distort the frequencies in every nearby band, creating an equalization entirely different from the preset. Therefore you should use it wisely and in moderation.

Parametric Equalizers

We will now look at parametric equalizers, which offer a more flexible control with respect to graphic EQ's, even if the procedure is a bit more complex.
With parametric equalizers you select the frequency on which to work. Generally, the controls are the following:

• frequency. With this control you can selecte the frequency that will be cut or emphasized using the "level"
• level. Checks the cut or the emphasis of the selected frequency with the "frequency" control.
• Q, or bandwidth. The bell curve is seen above. This control determines how wide or narrow the bandwidth has to be (how much it will influence the frequencies near the selected bandwidth). A narrow bandwidth increases or cuts the nearby frequencies, while a wide bandwidth influences even more frequencies than before.

To reduce the volume of this frequency, you apply a negative value to the slide .

Finally we narrow the bandwidth in order to modify the preselected frequency without changing the others nearby.

Recommendations for use

The equalizer is generally connected after the compressor and before the pedal effects (if present). A rack equalizer should be connected after the preamp and compressor but before the effects. A sererate discussion deals with the connection of the send-return: if it is in series it can be connected, but in parallel absolutely not! This is because a send-return in series allows the entire signal to pass, while in parallel even a signal dry (without effect) is allowed to pass, and because of this the equalizer could not work on the entire signal. We will talk more about the send-return later.
A good system to use a pedal equalizer is one that uses the overdrive in a similar way (the previously seen system to get more sound), raising the volume of the middle frequencies (between 500hz and 1Khz). With graphic equalizers the relative slides are raised, while for parametric equilizers the control level of these frequencies are raised to their maximum. The other frequencies will remain "flat" (term used to indicate that the slide control is set to 0).
The results of this operation are the following: with the pedal disconnected the sound is normal with respect to the set sound (for this example, we will use a sound slightly distorted by rhythmics). Inserting the pedal the middle frequencies increase, which causes an increase of saturation and a higher sound presence, clearly useful for a solo. Reducing the middle frequencies to a negative value, you can go from an initial sound that is slightly distorted (pedal disconnected) to a slightly cleaner sound (pedal inserted), useful for crunch arpeggios. Some amplifiers and programmable preamplifers incorporate this system of pre-equalization with the other controls.
A similar system can be made by directly inserting a circuit on the guitar that checks the various selected frequencies and inserts them through a selector on the body of the instrument (EMG and Levinson are excellent).
The purpose of the equalizer should always be to improve an already good sound. As with any effect, abuse will only bring negative results, seeing the sound comes from the amplifier. Remember to use the advantages of the amplifier, and that experimentation is always good.
Concluding, it can be said that the choice of equalizer is extremely subjective, as it is for many types of effects. If the parametric equalizer is more powerful, precise and versatile, the graphic equalizer is surely more simple and immediate. Some believe that the parametric equalizer is more "cold", while the graphic equalizer is more guitar-friendly. The overall choice is yours: if possible, try both types of equalizers considering the combinations that will be done from there. Whatever choice you make, it should always be personally satisfying.