- Some History
- Dating
as far back as the 1930's, the equalizer is the oldest and probably the
most extensively used signal processing device available to the
recording or sound reinforcement engineer. Today there are many types
of equalizers available, and these vary greatly in sophistication, from
the simple bass and treble tone control of the fifties to advanced
equipment like the modern multi-band graphic equalizer and the more
complex parametric types. Basically, an equalizer consists of a number
of electronic filters which allow frequency response of a sound system
or signal chain to be altered. Over the past half century, equalizers
design has grown increasingly sophisticated. Designs began with the
basic 'shelving filter', but have since evolved to meet the
requirements of today's audio industry.
- Understanding EQ
and its Effects on Signals
- There are two areas of equalization that I want to cover. Those two
areas are vocals and music. I'd like to discuss the different effects of
frequencies within audio signals. What do certain frequencies do for sound
and how we understand those sounds. Why are some sound harsh? Why do things
sound muddy? Why can't I understand the vocals? I'll try and answer all
of these question and hopefully bring some light to the voodoo world of
EQ.
- Vocals
- Roughly speaking, the speech spectrum may be divided into three main
frequency bands corresponding to the speech components known as fundamentals,
vowels, and consonants.
- Speech fundamentals occur over a fairly limited range between about
125Hz and 250Hz. The fundamental region is important in that it allows
us to tell who is speaking, and its clear transmission is therefore essential
as far as voice quality is concerned.
- Vowels essentially contain the maximum energy and power of the voice,
occurring over the range of 350Hz to 2000Hz. Consonants occurring over the
range of 1500Hz to 4000Hz contain little energy but are essential to intelligibility.
- For example, the frequency range from 63 to 500Hz carries 60% of the
power of the voice and yet contributes only 5% to the intelligibility.
The 500Hz to 1KHz region produces 35% of the intelligibility, while the
range from 1 to 8KHz produces just 5% of the power but 60% of the intelligibility.
- By rolling off the low frequencies and accentuating the range from
1 to 5KHz, the intelligibility and clarity can be improved.
- Here are some of the effect EQ can have in regards to intelligibility.
Boosting the low frequencies from 100 to 250Hz makes a vocal boomy or chesty.
A cut in the 150 to 500Hz area will make it boxy, hollow, or tube like.
Dips around 500 to 1Khz produce hardness, while peaks about 1 and 3Khz
produce a hard metallic nasal quality. Dips around 2 to 5KHz reduce intelligibility
and make vocals woolly and lifeless. Peaks in the 4 to 10KHz produce sibilance
and a gritty quality.
- Effects of Equalization on Vocals
- For the best control over any audio signal, fully parametric EQ's are
the best way to go.
80 to 125
160 to 250
315 to 500 |
Sense of power in some outstanding bass singers.
Voice fundamentals
Important to voice quality |
630 to 1K |
Important for a natural sound. Too much boost in the
315 to 1K range produces a honky, telephone-like quality. |
1.25 to 4K
5 to 8K |
Accentuation of vocals
|
- Important to vocal intelligibility - Too much boost between 2 and 4KHz can mask certain vocal sounds such as 'm', 'b', 'v'.
- Too much boost between 1 and 4KHz can produce 'listening fatigue'.
- Vocals can be highlighted at the 3KHz area; at the same time, dip the instruments at the same frequency.
- Accentuation of vocals:
- The range from 1.25 to 8K governs the clarity of vocals. Too much in the area of 5 to 16K can cause sibilance.
- Instruments
- Mic'ing instruments is an art ... and equalizers can often times be
used to help an engineer get the sound he is looking for. Many instruments
have complex sounds with radiating patterns that make it almost impossible
to capture when close mic'ing. An equalizer can compensate for these imbalances
by accenting some frequencies and rolling off others. The goal is to capture
the sounds as natural as possible and use equalizers to straighten out any
non-linear qualities to the tones.
- Clarity of many instruments can be improved by boosting their harmonics.
In fact, the ear in many cases actually fills in hard-to-hear fundamental
notes of sounds, provided the harmonics are clear. Drums are one instrument
that can be effectively lifted and cleaned up simply by rolling off the
bass giving way to more harmonic tones.
- Here are a few ideas on what different frequencies do to sounds and
their effects on our ears.
40Hz to 70Hz |
These frequencies give music a sense of power. If over emphasized they
can make things muddy and dull. Will also cloudy up some harmonic content. |
80Hz to 125Hz |
Too much in this area produces excessive 'boom'. |
160Hz to 250Hz |
This is the problem area of a lot of mixes. To much of this area can
take away from the power of a mix but is still needed for warmth. 160Hz
is a pet-peeve frequency of mine. Also, the fundamental of bass guitar
and other bass instruments sit here. |
300Hz to 500Hz |
Fundamentals of string and percussion instruments. |
400Hz to 1K |
Fundamentals and harmonics of strings, keyboards and percussion. This
is probably the most important area when trying to control or shape to
a natural sound. The 'voice' of an instrument is in the mids.
To much in this area can make instruments sound horn-like. |
800Hz to 4K |
This is a good range to accentuate instruments or warm them up. Too
much in this area can produce 'listening fatigue'. Boosts in the 1K to
2K range can make instruments sound tinny. |
4K to 10K |
Accentuation of percussion, cymbals, and snare drum.
Playing with 5K makes the overall sound more distant or transparent. |
8K to 20K |
This area is often what defines the quality of a recording or mix.
This area can also help define depth and 'air' to mix. Too much can take
away from the natural sense of a mix by becoming shrill and brittle. |
-
- Here are a few other pin point frequencies to start with for different
instruments. In a live sound situation, I might preset the console's
eq to these frequencies to help save time once the sound check is under
way. These aren't the answers to everything... just a place to start at.
- Kick Drum:
- Besides the usual cuts in the 200Hz to 400 area, some tighter bandwidths
at 380Hz, 5kHz and shelf at 10k may help. The point of these frequencies makes for space
for the fundamental tones of a bass guitar or stand up. I have also found
a high pass filter at 40Hz to 50Hz will help tighten up the kick along with giving
your compressor a signal it can deal with musically.
- Snare Drum:
- The snare drum is an instrument that can really be clouded by having
too much low end. Frequencies under about 150Hz are really un-usable for
modern mixing styles. I would suggest a high pass filter in this case.
Most snares are out front enough so a few cuts might be all that is needed.
I like to start with 260Hz, boost at 5kHz, and some 12K. This are just frequencies
to play with. Doesn't mean you will use all. If the snare is too transparent
in the mix but I like the level it is at, a cut at 5K can give it a little
more distance and that might mean a little boost at 10K to brighten it
up.
- High Hats:
- High hats have very little low end information. I high pass at 200Hz
can clean up a lot of un-usable mud in regards to mic bleed. The mid tones
are the most important to a high hat. This will mean the 400Hz to 1K area
but I've found the 600Hz to 800Hz area to be the most effective. To brighten
up high hats, a shelving filter at 12.5K does nicely.
- Toms and Floor Toms:
- Again,
the focus here is control. I like to high pass at 100Hz which give more
focus about tone rather than size. Most toms could use a cut in the
300Hz to 400Hz area. And there is nothing real usable under 100Hz for a
tom... unless you are going for a special effect. Too much low end
cloud up harmonics and the natural tones of the instrument. Think color
not big low end. Boost at 5kHz and shelf at 10kHz to make things more
aggressive. .
- Over Heads:
- In my opinion, drum over heads are the most important mics on a drum
kit. They are the ones that really define the sound of the drums. That
also give the kit some ambience and space. These mics usually need a cut
in the 400Hz area and can use a good rolling off at about 150Hz. Again,
they are not used for power.... these mics 'are' the color of your drum
sound. Roll off anything that will mask harmonic content or make your drums
sound dull. Cuts at 800Hz can bring more focus to these mics and a little
boost of a shelving filter at 12.5K can bring some air to the tones as
well.
- Bass Guitar:
- Bass guitar puts out all the frequencies that you really don't want
on every other instrument. The clarity of bass is defined a lot at 800Hz.
Too much low end can mask the clarity of a bass line. I've heard other
say that the best way to shape the bass tone is to roll off everything
below 150Hz, mold the mids into the tone you are looking for, then slowly
roll the low end back in until the power and body is there you are looking
for. If the bass isn't defined enough, there is probably too much low end
and not enough mid range clarity. Think of sounds in a linear fashion,
like on a graph. If there is too much bass and no clarity, you would see
a bump in the low end masking the top end. The use of EQ can fix those
abnormalities. High pass at 40Hz to 50Hz to tighten things up. .
- Guitar/piano/ etc.:
- These instruments all have fundamentals in the mid range. Rolling off
low end that is not needed or usable is a good idea. Even if you feel you
can't really hear the low end, it still is doing something to the mix.
Low end on these instruments give what I call support. The tone is in the
mids. 400Hz and 800Hz are usually a point of interest as are the upper
mids or 1K to 5K. Anything above that just adds brightness. Remember to
look at perspective though. Is a kick brighter than a vocal? Is a piano
bright than a vocal? Is a cymbal brighter than a vocal?
- In Closing
- Equalizers are one of the most over looked and mis-used pieces of gear
in the audio industry. By understanding equalizers better, an engineer
can control and get the results he or she is looking for. The key to EQ'ing
is knowing how to get the results you are looking for. Also, knowing if
its a mic character or mic placement problem. EQ can't fix everything.
It can only change what signal its working with. Equalizers are also a
lot more effective taking away things in the signal than replacing what
was never there.
- Written by Devin DeVore
- © TSC / TRINITY SOUND COMPANY
- Additional research provided by Klark - Technik
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