This article comes from the wonderful Ziggy's sonorisation site. It is reproduced here, of course, with the kind permission of Ziggy himself ;o) We really advise you to go to this site, where you will find other articles that don't have their place here, especially concerning microphones, mixing boards, amplifiers, etc.

Drums
Bass
Guitar
Voice and others
Mastering
Frequencies

The equalization enables to influence and to master the sound colour of an instrument or a mix. It is also used to balance a mix, i.e. to help each instrument to find its place in the sound spectrum. During live shows, it is used to avoid feedback, and to impose a certain sound colour, or to attenuate the sound defects of a concert hall.

There are two sorts of EQ:

The graphic EQ, where the frequencies spectrum is cut in a certain number of bands. The more simple is the 2 or 3-band EQ which can be found on guitar amp and radios or small Hi-Fi. A little more sophisticated, still on amps, or on some mixing boards, the 6-band EQ, where six different settings can be found. However, for serious work, 15 bands are needed. The standard in live and studio is 31 bands. We are then talking of a third octave EQ, since very octave is divided in three bands.
The other family is composed of parametric EQ. Here, frequencies and bandwidth are not fixed, but can be freely set. SI, if you want to affect the 1.5kHz and if you only have a 15-band EQ, you will have to choose between the nearest pre-settings, 1kHz in our case, and it will affect the whole frequency range between 500 Hz and 2 kHz. The result won't be the same if you use a parametric EQ and if you set the exact frequency (1.5 kHz) with a sufficiently narrow width in order to affect only frequencies between 1.4 and 1.6 kHz!

Main settings on EQ

Graphic Eq

INPUT - Input level, in order to not saturate the electronic circuits.
LOW CUT - High-pass filter, to make a first filtering (low frequencies will be attenuated under a certain frequency)
HIGH CUT - Low-pass filter, to make a first filtering (high frequencies will be attenuated above a certain frequency). On some models, we can find noise limiter or reducer (dBx 2231)
LEVEL - The input level setting is often replaced by an output level setting in order to correct the gain changes on the modified signal. (if you increase by 6 dB the 1kHz, the sound volume will almost double!).Then, there are the different cursors or pots to increase or decrease the frequencies.
RANGE - Good quality EQs have a switch to change the maximum setting extent between 6 dB (finer) and 12 dB (more efficient)
BYPASS - It is essential to compare the direct sound and the processed sound.

Parametric EQs

INPUT - Input level, in order to not saturate the electronic circuits.
LOW CUT - High-pass filter, to make a first filtering (low frequencies will be attenuated under a certain frequency)
HIGH CUT - Low-pass filter, to make a first filtering (high frequencies will be attenuated above a certain frequency). On some models, we can find noise limiter or reducer (dBx 2231)
OUTPUT - The input level setting is often replaced by an output level setting in order to correct the gain changes on the modified signal. (if you increase by 6 dB the 1kHz, the sound volume will almost double!).Then, there are the different cursors or pots to increase or decrease the frequencies.
FREQUENCY - Sets the central frequency
BANDWITH or Q - Sets the width of the band. Numbers refer to octave, 2 means a width of 2 octaves (for 1 kHz the bandwidth goes from 500 Hz to 2 kHz), 0.5 means half an octave (for 1kHz, it goes from 800 Hz to 1.2kHz). But be careful, on some devices, the numbers exactly indicate the contrary, i.e. 2 means half an octave and 0.5 means 1/0.5 = 2 octaves
LEVEL - Set the process gain, generally from -15 to +15 dB
BYPASS - It is essential to compare the direct sound and the processed sound.

Know that in order to make a good equalization work, you must have quality devices! A 90 €uros 15 bands EQ bought in a supermarket is no earthly use. It will only bring noise and distortion!!!

Let's see now some practical examples of use (these propositions are rather arbitrary, the ears will choose at the end!).

Drums

On the Bass Drum, we will try to give a good foundation for the warmth and the woumm, and we will increase the low-medium for the kick which characterize the modern sound.

Low + 4 to 6 dB at 80 Hz
Low - 2 to 4 dB at 150 Hz
Low-medium - 4 to 6 dB at 630 Hz
Medium + 6 to 10 dB at 3 kHz

On toms, we will attenuate the low-medium which sounds like "ploc" et we increase the low and high harmonics if possible, because some badly set toms resonate a lot in low frequencies, and we must cut these ones to the detriment of the sound.

Low + 2 to 5 dB at 180 Hz
Low-medium - 4 to 8 dB at 630 Hz
Medium + 4 to 6 dB at 2,5 kHz
High + 2 dB at 5 kHz

On the snare drum, the settings are different depending on what we want to obtain.

Fine Snare Drum (jazz, funk) :

Low + 2 to 4 dB at 180 Hz
Low-medium - 4 dB at 630 Hz
Medium + 4 to 6 dB at 4 kHz
High + 5 dB at 10 kHz

Medium Snare Drum (funk, dance) :

Low + 2 to 5 dB at 250 Hz
Low-médium + 3 to 5 dB at 1,2 kHz
Medium + 4 to 6 dB at 3 kHz
High + 2 dB at 10 kHz

Snare Drum (rock, light music) :

Low + 2 to 5 dB at 200 Hz
Low-medium - 4 to 8 dB to 630 kHz
Médium - 2 à 5 dB à 1,5 kHz
High + 6 dB at 6 kHz

Heavy Snare Drum (rock, heavy) :

Low + 4 to 10 dB at 230 Hz
Low-medium - 2 to 5 dB at 500 Hz
Medium + 2 to 5 dB at 2,5 kHz
High + 6 dB at 4 kHz

Hi-hats and cymbals (overhead)

Low - 12 dB à 250 Hz
Low-medium - 6 dB at 800 Hz
Medium - 2 dB at 2kHz
High + 2 to 4 dB at 8 kHz

Bass

Increase the low and high harmonics:

Low + 2 to 5 dB at 100 Hz
Low-medium - 3 dB at 800 Hz
Medium + 2 to 4 dB at 2 kHz
High - 8 dB at 10 kHz
Low pass at 8 kHz

Electric guitar

I am often confronted with two major problems, especially with saturated guitars. First, the sound is too mat and coated: decrease a little the 400 Hz and increase the 2-3 kHz. Secondly, the sound is too aggressive: attenuate the 2-3 kHz.

Clean sound (funky)

Low + 4 dB at 250 Hz
Medium - 4 to 6 dB at 800 Hz
High + 2 to 4 dB at 4 kHz

Clean sound (blues)

Low + 4 dB at 250Hz
Medium + 4 dB at 1,2 kHz
High + 2 dB at 4 kHz

Saturated sound (blues, lead)

Low +4 dB at 250Hz
Medium +4 dB at 1,2 kHz
High + 2 dB at 4 kHz

Saturated sound (modern heavy)

Low +10 dB at 180Hz
Medium - 6 dB at 800 Hz
High + 6 dB at 4 kHz

Acoustic guitar

Low +4 to 6 dB at 160 Hz
Low-medium - 4 dB at 500 Hz
Medium -2 dB at 1,6 kHz
High + 2 to 4 dB at 6 to 8 kHz

Voice

To attenuate a little the low-medium and increase the high-medium is a good thing to emphasize the voice.

High-pass filter at 100 Hz
Low + 2 dB at 200 Hz
Low-medium - 2 to 4 dB at 350 Hz
Medium + 4 to 6 dB at 2 kHz
High + 2 dB at 5 kHz

Brass, Woodwinds and Keys

There is often no need to equalize - on saxophones and flutes, we will sometimes attenuate high-medium (2 to 4 kHz).

General mix

A complete mix is always very delicate to process, because the signal is very complex. Avoid the "V" setting (i.e. low and high frequencies to the max, medium to zero), it sounds powerful but always makes think of a bad disco sound. Rather try to emphasize the harmonics and to make the colour being more interesting by finding the important frequencies (frequencies which change the sound spectrum as soon as you touch them). To attenuate low medium and increase brightness is often fabulous.

Low + 3 dB at 80 Hz
Low-medium - 3 dB at 350 Hz
Medium - 2 dB at 2 kHz
High + 2 to 4 dB at 12 kHz

EQ in the mix

The EQ can be useful to balance a mix. If for example we equalize all the instruments with the same settings (low to the max, medium to zero), we will obviously obtain a big "noise". Instead of separately treating the instruments, try to attribute them a place in the mix depending on their colour and frequencies, avoiding too much overlapping in frequencies.

Example : if the bass drum is very heavy and powerful in the 80 Hz, don't do the same for the bass, attenuate the 80 Hz, and increase a slightly higher frequency, 150 Hz for example.

Same thing for the guitar. It doesn't need to have low frequencies to the max, it would only heavy the mix. On the contrary, attenuate the medium around 60 - 800 Hz, the low will automatically sound warmer, and if you increase a little the 2.5 kHz, the guitar will easily place itself on the front line.

Same thing for the voice. Don't put too much low frequencies, otherwise the mix will be coated...

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Frequency table

Here is a little referential table, which gives information on the important frequencies of instruments.

Instruments	Low-cut	Fundamental	Sensitive frequency	Harmonics
These frequencies are obviously given for information only, and have to be refined depending on cases...
Male voice	100 Hz	200 Hz	2 kHz (+)	4 to 5 kHz
Female voice	120 Hz	300 to 400 Hz	2,5 kHz	5 to 6 kHz
Spoken voice	120 Hz	200 Hz	2 to 3 kHz	4 kHz
El. guitar	80 Hz	200 to 300 Hz	2,5 kHz	> 4 kHz
Ac. Guitar	100 Hz	150 to 250 Hz	2 to 3,5 kHz	6 kHz
Piano	-	80 to 150 Hz	2 to 3 kHz	> 4 kHz
Harmonica	100 Hz	250 Hz	1,5 to 2,5 kHz	4 kHz
Saxophone	80 Hz	150 to 250 Hz	2 kHz (-)	3 to 4 kHz
Trombone	80 Hz	150 Hz	1,5 kHz	3 kHz
Trumpet	120 Hz	300 Hz	1,5 kHz (-)	> 4 kHz
Flute	200 Hz	300 Hz	1,5 to 2 kHz	4 kHz
Bass	-	80 Hz	250 to 500 Hz	2 to 3 kHz
Bass Drum	-	60 to 80 Hz	350 to 600 Hz (-)	2 to 3 kHz
Snare Drum	80 Hz	150 to 250 Hz	600 to 1,5 kHz	3 to 5 kHz
Tom	100 Hz	150 to 200	600 (-)	2 to 3,5 kHz
Floor Tom	-	120	300 to 500 (-)	2 to 3,5 kHz
Hi-Hats/Cymbals	200 Hz	400 to 600 Hz	2 to 3 kHz (-)	8 kHz
First, a very important thing: in order to work well on equalisation, a parametric eq is essential!! Thus, on small mixing boards, frequency ranges are often fixed (medium to 2kHz for example). These frequencies are rather well chosen in order to equalize a voice or a guitar, but inappropriate for drums. The first column gives the frequency of a possible LOW CUT, that is to say the low frequencies which are relatively useless for the instrument sound. Professional mixing board have a low cut (which sometimes can be set, or with a fixed frequency, 100 Hz for example), with which all the useless low frequencies are removed. This considerably lighten the whole mix, and remove many parasitic noises. The FUNDAMENTAL column gives the frequency on which the instrument is based. Increasing it, we can find immediately warmth and depth; decreasing it, the sound lightens and becomes slighter. SENSITIVE FREQUENCY is the mainspring frequency of the instrument. It is the critical frequency which will the more influence the sound. Increasing it, the instrument seems louder and will naturally place in front of the mix, but this can quickly become aggressive. Decreasing it, the instrument goes "inside" the mix and the sound softens. HARMONICS gives the frequencies which are responsible for the colour of the instrument sound. Increasing it, we have the impression of more presence and brightness, decreasing it the sound becomes dull.