Equalization is a powerful tool for evening out the tone of
instruments and mixes, as well as giving instruments an "edge" to
their sound. If, for instance, a resonance in the instrument gives
it a funny color, reducing the frequency of the resonance gives a
much more even and desirable sound.
The classic example of this is a resonance that can occurs when you
put a microphone inside a kick drum. The resonance (at about 400 Hz)
tends to make the kick drum sound like a big oatmeal box. When you
listen to the kick from a distance it doesn't sound like a Quaker
Oats instrument, but the sound picked up microphone sure does.
Reducing 400 Hz with EQ smoothes it right out and gives you a very
present sound without the cardboard.
In the kick drum example the microphone placement amplified
frequencies that were being generated by the drum. There are other
situations that occur in recording where an extra sound at a
particular frequency (called a "formant") is generated and is not
really part of the sound generation mechanism. These don't
necessarily respond well to using equalization alone.
One example of this kind of situation is the "S" sound generated by
singers when pronouncing the S. The air rushing through the teeth
make a spike at about 7-8kHz. This only occurs when the singer sings
a "S." Reducing 7 kHz with EQ reduces this frequency's level when
the singer is singing the "S" but also when they aren't. Since 7 kHz
is close to the "presence" frequency you wind up with a dull vocal -
something that cannot happen in a mix.
Another example of this situation is the microphone "pop" that can
occur with close-micing a vocal. The blast of air generated by the
vocalist pronouncing hard consonants (P, B, D, etc.) make very
low-frequency thumping sounds - microphone "pops". Again this
cannot be removed with standard EQ without adversly affecting the
tone of the overall vocal.
The Dynamics Processing Side Chain
The side Chain input of a dynamics processor (offten called a "key"
input) can be used to reduce level during vocal S's and mic pops.
The side chain is the control circuit of the dynamic processor. The
dynamic processor changes gain according to the signal sent to the
side chain. In a normal configuration the input to the dynamic
processing also feeds the side chain. But if the dynamic processor
has a "key" input, putting a signal into that input make it respond
to that signal, not the input signal.
You can buy deessers. A deesser is a dynamics processing unit that
has an equalization inserted into the sidechain that boosts 7 kHz.
Now the unit will reduce gain whenever there is a spike at 7 kHz.
Since it is only in play when there is an "S" it leaves the vocal
alone at any other time. A Deesser can be built in a DAW program by
creating an aux track that has a boost at 7kHz and then feeding this
into the key input of a compressor via a buss.
this configuration, you can also handle other problems like vocal
pops, simply by changing the frequency of the control equalization -
the "equalization envelope." For vocal pops, use a boost at 50 Hz,
with shelf equalization.
Why Not Just Buy a Dessser?
There are hardware solutions and you can even get plug-ins that will
do deessing and even "tune" the frequency of the equalization
envelope controlling the gain reduction. In today's DAW programs,
the addition of an outboard hardware unit is extra gear that the
sound has to go through and you'll probably have to convert your
digital recording to analog and then back to digital. This much
alteration of the signal will also noticably degrade the signal. As
far as another plug-in - why spend the money when you can make a
deesser, depopper, etc when you can make youer standard plug-ins do
the job and even get a better result for your particular production?
Usually large boosts of the frequency you use as your equalization
are desirable. Higher Q values (between 2 - 4) also help you isolate
the gain reduction to just the problem spikes.
Anytime you have a note or a sound that is repeatedly loud, an
equalization envelope in a dynamics processor is a way you can
correct this annoying problem. Here's a list of some of the
equalization envelopes I have used successfully in mixing:
7 kHz - Deessing
50 Hz - Removing vocal pops
4 kHz - Evening out a sax part
100 Hz - Evening out a bass line
Using A Spectrum Analyzer
One of the tools that most DAW setups have (or should have) is a
spectrum analyzer program. This program will show you the energy in
the audio at different frequencies.
You can take any track and look at it playing the part. If the line
is uneven, you will see a frequency spike anytime a particular pitch
is played. You also can see, for instance, the exact frequency that
the annoying "S" is at - and this varies from singer to singer.
Using this tool can let you exactly tune the equalization envelope
to what you need.
Ozone3 Spectrum Analysis
Next week I will publish some audio demos and Pro Tools setups for
using equalization envelopes - stay tuned.