Equalization is the most-used, most-mis-used, most-over-used and most-under-used signal processing device. It is also the most powerful. By definition an equalizer is a gain control that raises or lowers gain at a specific set of frequencies without affecting the gain at other frequency ranges.
I learned a lot about equalization by sitting down with a graphic equalizer and lots of records. After about 30 hours of listening to the effect of different bands of equalization on the records, I began to “hear” the effect of certain frequencies on overall mixes. Since I had a job in mastering, this was a direct application as to how I was going to use equalizers.
Doing an exercise like this is the very beginning of training in using equalization. There are commercial CD packages which attempt to duplicate this type of test. They are no real substitute for switching the equalization on and off as the CD (or music source) plays.
The next step in the training is to apply specific equalization to specific instruments. Recommended or “key” frequencies are used and the equalization is switched on and off while soloing the instrument and then while listening to the instrument in the mix.
The point of this “ear” training is to gain the ability to hear what frequencies would be needed to bring up or down in a specific mixdown. Until one obtains the ability to “hear” frequency, one has only limited ability to use equalization.
A key to understanding equalization is to gain an understanding of the effect of different frequency ranges on music and instrument sounds.
The “First Octave”
The first usable octave for most recording is the 40 – 80 Hz range, with equalization settings centered around 50 Hz. This range of frequencies is often referred to as “Low Bass”
There is sound between 20 Hz and 40 Hz but little or no sound from instruments. The lowest pipes of a pipe organ will get into this range but more “ordinary” instruments like Bass Guitar, Upright Bass and Foot Drums do not. The lowest pitch on a bass guitar or string bass is at 41 Hz. Thunder, earthquakes and rumble from the building shaking extend below 40 Hz. While mixing, watch out for objectionable sounds below 40 Hz caused by building shifts and mic stands moving with heavy footsteps. If there is objectionable sounds in this range, the range can usually be taken entirely out with a filter.
The first octave that we deal with (40 – 80Hz) gives more of a “feeling” and sense of “power” to the sound. This range is way down or non-existent in smaller stereo systems. This range is difficult to hear at all at medium and low volume levels because of the Fletcher Munson Effect.
To properly set the amount of low bass in your mix or in your instrument sound, you must listen both loud and soft. You also may want to listen to the mix or instrument on large and small speaker systems. Too much energy in this range will make the mix sound muddy on large speakers played loud and still sound good on small speakers played at a medium volume. You want the mix or instrument to sound larger and more powerful over large speakers without sounding muddy.
Rap, Hip Hop and “Dance” music (under various names) often have extra energy in the low-bass range. This is what causes cars equipped with sub-woofers to shake. Usually, however, it is not the entire mix that is boosted below 80 Hz, but just, for example, the foot drum. By boosting the energy on only one or two instruments, “clarity” can be achieved without “mud.”
The Bass Range
Covering about 1.5 octaves, from 80 Hz to 250 Hz, this range of frequencies determines the “fatness” and “fullness” of the instrument’s sound. Equalization is usually applied centered around two frequencies, 100 Hz and 200 Hz.
For guitars and bass, the 100 Hz range tends to add body and fullness. Excessive energy in this range tends to make these instruments sound “boomy.,” This range of frequencies is still greatly affected by the Fletcher-Muson Effect; this means you will need to listen to the mix and instrument both loud and soft. Similar to how the 50 Hz range affects the bass and foot, the guitars should sound fatter when played loud, not boomy. Reducing the 100 Hz energy on the guitar will usually cause distinction between the bass and guitar parts. The lowest fundamental frequency on a guitar is around 80 Hz.
For vocals the 200 Hz range determines the fullness of the vocal. This range can often be reduced to increase distinction on the vocal. If, however, boosting in higher frequencies on the vocal makes the sound “thin” or “small” a boost of 200 Hz. will restore fullness.
When 100 Hz is reduced on a guitar or bass to reduce “boom,” at small boost at 200 Hz can be helpful to keep the instrument from sounding “lumpy” (certain notes hard to hear and others standing out). The guitar and bass have almost equal energy at their fundamental and 2nd harmonic frequencies. Thus if a range of notes becomes hard to hear because of a at lot of 100 Hz, reducing energy at 100Hz and adding energy at 200 Hz will help the notes be heard again.
The Bass Presence / Lower Mid Range
Covering about one octaves from 250 Hz to 500 Hz, this range accents ambience of studio and adds clarity to the bass and lower-string instruments (Cello and Upright Bass). Too much boost can make higher-frequency instruments muffled sounding and low-frequency drums (foot and toms) have a cardboard box quality. Equalization in this range is applied at many frequencies but most often between 300 Hz and 400 Hz.
The lower part of this range (250 Hz to 350 Hz) is sometimes referred to as “Upper Bass” and is used to increase distinction and fullness on the vocal, especially on female singers.
The Lower Mid Range in general can be viewed as the “Bass Presence Range” Increasing this range gives clarity to the bass line and the lower-register of pianos and organs. Clarity and distinction can be obtained between the foot drum and bass guitar by both reducing the foot and increasing the bass guitar in this range, at the same frequency.
This range is often reduced for overhead drum and cymbal microphones to increase clarity and presence on these instruments’ and reduced on lower drums (foot and toms) to reduce boxiness.
The Mid Range
The Mid Range band of frequencies covers two octaves from 500 Hz to 2 kHz. This range can give a horn-like quality to instruments (500 Hz to 1 kHz) and a “tinny” sound (1 kHz to 2 kHz) or a telephone-like quality (all of the range). Equalization usually centers around 800 Hz and 1,.5 kHz.
The mid-range also tends to accent the presence (800 Hz) and attack (1.5 kHz) of the bass guitar. The lower pitches of a rhythm guitar can be given more attack by a boost at 1.5 kHz.
For your Mid Range Instruments (vocals, guitars and piano) this range is most-often reduced rather than accented. Reducing 500 – 800 Hz on an acoustic guitar can remove the “cheep” sound and make it sound more “silvery.” Reducing 800 Hz on a vocal makes it sound less nasal and have more body and presence. For snare drums, a reduction of 800 Hz can take the tinny, cheep sound out of the drum and make the snares have more sizzle rather than rattle.
The Upper Mid Range
Covering about one octave, this range of frequencies is responsible for the attack on percussive and rhythm instruments and the “projection” of mid range instruments. Equalization can be applied at any frequency in this range but still somewhat centers around 3 kHz.
On the foot drum, boosting 2.5 kHz or 4 kHz increases the attack. 2.5 kHz sounds more like a felt beater and 4 kHz sounds more like a hard-wood beater. These frequencies can also be used to increase the attack or “hit” sound on toms and snare drums.
Guitar lines often get more attack and distinction with equalization added at this range. A small boost (1-3 dB) for the vocal will increase projection. Adding too much energy, in this range, makes it hard to distinguish the syllables of the vocal and can cause listening fatigue. This range of frequencies is often reduced on background vocal to give them a more “airy” and “transparent” sound.
The Presence Range
Although this range covers a mere half-octave of 4 kHz to 6 kHz, it is an often-used band of frequencies. This range makes most vocals and melody instruments sound closer and more distinct. Over-boosting causes a irritating and harsh sound. Equalization centers around 5 kHz.
The Treble Range
Covering approximately that last two octaves of sound (6 kHz to 20 kHz), this band of frequencies is responsible for the brilliance and clarity on instruments. Equalization centers around 7 kHz, 10 kHz and 15 kHz.
The vocal “S” sounds are at about 7 kHz, making this a frequency that is avoided for vocals. Care must be exercised in reducing 7 kHz on vocals, however, because the vocal will sound dull very fast. The breath sound of the vocal is at 15 kHz and above, giving a breath quality without much accent on the “S”: sound of the vocal.
The 7 kHz frequency is also the “metallic attack” frequency on drums The “sizzle” of cymbals is at 15 kHz.
When equalizing, 10 kHz and above is often used as a general “brilliance” frequency band.