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
Understanding EQ and its Effects on
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
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
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
Important to voice quality
630 to 1K
Important for a natural sound. Too much
boost in the
315 to 1K range produces a honky,
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 and at the same time dipping 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
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
Here are a few ideas on what different frequencies do to sounds
and their effects on our ears.
31Hz to 50Hz
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
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
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
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
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 event
pre set 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.
Besides the usual cuts in the 200Hz to 400 area, some tighter Q
cuts at 160Hz, 800Hz and 1.3k may help. The point of these cuts
makes for space for the fundamental tones of a bass guitar or stand
up. I have also found a high pass filter at 50Hz will help tighten
up the kick along with giving your compressor a signal it can deal
with musically. 5K to 7K for snap.
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 400Hz, 800Hz, and
some 1.3K. 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 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. Most toms could use a cut in
the 300Hz to 800Hz 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.
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 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
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?
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 -