It can be used to remove unwanted frequencies that might
be to harsh sounding or that are interfering with other sounds in the
mix. It can also be used to reduce tape hiss from cassette tapes (see
High Shelf EQ).
For instance if there is a low rumble in the recording,
caused by being to near a truck roadway, you can easily get rid of it
through the use of an EQ. Use a low shelf eq to
remove the rumble.
To use your eq(s) effectively you should map out the
sounds you currently are trying to mix together. You can take a look at
this chart for a reference of
instrument type and frequency range.
EQs can be found on mixing desks, effects processors and
audio software.
Low Shelf
/ Low Pass Filter (LPF) – only allows low frequencies
through. It behaves similarly to a bass knob on your stereo. Low Shelf
EQ’s effects (boost or cut) the amplitude of frequencies starting at
the selected frequency and then everything below it.
High Shelf / High Pass Filter (HPF)
– basically only allows high frequencies through. It behaves similar
to a treble knob on a stereo. High Shelf EQ’s effects (boost or cut)
the amplitude of frequencies starting at the selected frequency and
then everything above it.
Peak Type/ Band Pass Filter / Notch Filter: (Most Normal)
– only allows a range of medium frequencies through. Boost or Cut a
selected frequency of a sound. You can't isolate a particular
frequency exactly but you can get pretty narrow. For instance say you
wanted to cut the frequencies around 250 Hz. You would effect the
frequencies from about 200 to about 300 hz for the most part. The
amount of frequencies effected by the eq is what is called it's 'Q'.
Adjusts the level of signal at the set frequency, and some surrounding
frequencies. The Q setting determines how many surrounding frequencies
are affected.
What the controls do:
Input (gain): adjusts the volume coming into the
EQ.
Frequency / Sweep: selects the frequency to be
effected.
Gain: boosts or cuts (decreases) the volume
within the selected frequency area.
Q / Width – This setting is what determine how large or
small the frequencies around the eq's frequency are affected (the size
of the bump, or hill in the EQ graph). This is also called Resonance or
Bandwidth. Sets the amount of surrounding frequencies that will be
affected. Octaves are used to help define more easliy how many
frequencies the eq is effecting.
Q setting reference chart:
Q Setting
|
Width
|
0.7
|
2 Octaves
|
1.0
|
1 1/3 Octaves
|
1.4
|
1 Octave
|
2.8
|
½ Octave
|
How to use the EQ:
First you should know what sounds (Instruments) are
going to used in the mix. You can get the guitar for instance to sound
really great but when you add the bass it sounds really muddy.
I generally go through each sound and apply eq (if it
needs it) to remove low end rumble or high end noise. This is a
SUBTRACTIVE process where there is NO boosting of any frequency. If you
are removing more than -6dB at any frequency then the problem should
have been taken care of by moving the mic or added baffles when it was
recorded. None the less you have to deal with what you've got.
While going through this initial survey of the sounds I
will try to make them sound better (without hearing any other
instrument) and also knowing already what frequencies of sound, the
guitar, interfere with other sounds, the bass.
I then find a place in the song where ALL the
instruments or as many instruments are playing at the same time.
What is the most predominant sound? The Voice? The
Guitar? Start with that sound. Make it sound as good you can by using EQ
only (no reverb, no delay, no chorus, no effects). This is to get
the overall sound correct. Then you can do levels and effects.
Next add next most predominant instrument. Listen and
see how it interacts with the most predominant sound. This is where your
ears need to be used. Listen for jumps in volume or for the annoying
frequencies, the ones that really stand out. Reduce those frequencies. You
will note that no frequencies have been boosted. At this point you want
to create a DRY and balanced mix.
Next add the third most predominant sound and continue
as previously. Obviously if you have many tracks this process can seem
too complex but it isn't. Just break down the tracks in to groups or
sub-mixes. Minimally do this to instruments that have a similar range
(Piano, Guitar, and Bass and Kick Drum).
At this point you can add Compression
to help even-out the peaks even more. The main thing is to get a
balanced mix by using EQ only. Do this without using any Reverb, Delay,
Chorus etc... The effects do colour the sound it is true but you need to
start with a good sound to make the effects sound good.
Instruments - Sound
Frequency Chart
below 20Hz- This is below what most humans are
capable of hearing. At very high volumes of the this frequency you feel
it.
below 40 Hz- These are very low frequencies that
are responsible for most muddy sounds. This frequency uses up most of
the bandwidth (power) of a power amp and speakers. Use this frequency
sparingly, also watch your meters. You see them get louder but you won't
hear a vast difference in the volume of your mix.
60Hz - kick drum, bass, hum. It's true that in
the US the frequency of 60 Hz really interferes with kick drums and bass
guitar frequencies. You boost this frequency and you boost the AC hum.
80Hz - bass guitar
120-180Hz - tom drums
200 Hz - the sharp attack sound of a bass guitar
250-300Hz -that annoying "cardboard
box" sound you get when recording things in a room, especially
drums.
1000Hz (1kHz) - first boost section of the human
voice. good for boosting voices in a film.
2000Hz (2kHz) - "Click" of a bass drum.
3kHz - best boost area of human voice, and great
for pushing a sound through a small speaker, use this to boost voices
for TV.
5 - 8 kHz - Sibilance (the "Sssss"
sounds produced by the voice).
above 10kHz- very high frequencies and main part
of audible hiss.
Above 20kHz- out of human hearing range (but not
bats, cats or dogs)
A note on hiss: Hiss is a sound that happens across all
frequencies at once. Therefore it is very hard to get rid of with a EQ,
you really need a special noise reduction processor or plug-in to do it.
But because of the way frequencies work there is more energy in the hiss
in the very high frequency area, so cutting this area will make the hiss
less obvious.
You can also try these articles on "How to Use
an Equalizer"
EQ
And Mixing Made Easy
Sound
system equalizing advice
The
Art of Equalization - a good basic introduction
Understanding
EQ and its Effects on Signals
Basics
of Equalization and Feedback
Constant-Q
and Equalizers - information on different equalizers, pdf document
Constant-Q
Graphic Equalizers - paper in pdf format
Crossovers,
Equalizers & Compressors - article in pdf format
EQ
- some history of equalizing and tips on using equalizers
Equalizing
Bass - bass does not usually translate to smaller speakers very well
without rolling out too much bottom
Signal
Processing Fundamentals - crossovers, equalizers and dynamic
controllers
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