PRESONUS StudioLive24.4.2 - Equalizers; What Is an EQ

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8.3 Equalizers
The StudioLive 24.4.2 is equipped with a 4-band parametric equalizer on every
input and output bus. Here’s a brief explanation of how an EQ functions, as well as
some charts to help you navigate the frequency ranges of various instruments so
you can quickly choose the best EQ settings for your recordings and live mixes.
8.3.1 What is an EQ?
An equalizer is a lter that allows you to adjust the level of a frequency,
or range of frequencies, of an audio signal. In its simplest form, an EQ will
let you turn the treble and bass up or down, allowing you to adjust the
coloration of, let’s say, your car stereo or iPod. In recording, equalization
is a sophisticated art. Good equalization is critical to a good mix.
When used correctly, an equalizer can provide the impression of nearness
or distance, “fatten” or “thin” a sound, and help blend or provide separation
between similar sounds in a mix allowing them to both shine through the mix.
Parametric EQ
The parametric EQ and semi-parametric EQ are the most common equalizers
found in recording and live situations because they oer continuous control
over all parameters. A parametric EQ oers continuous control over the audio
signal’s frequency content, which is divided into several bands of frequencies
(most commonly three to seven bands). A fully parametric EQ like those in the
StudioLive 24.4.2 oers control over the bandwidth (basically, the range of
frequencies aected), the center frequency of the band, and the level (boost/
cut) of the designated frequency band. It also oers separate control over the Q,
which is the ratio of the center frequency to the bandwidth. A semi-parametric
EQ provides control over most of these parameters but the Q is xed. Some
devices, such as the StudioLive 16.4.2, have quasi-parametric EQ, which is semi-
parametric EQ with a simple, switchable Q setting (typically, High and Low Q).
Q
Q is the ratio of center frequency to bandwidth, and if the center frequency
is xed, then bandwidth is inversely proportional to Q—meaning that as
you raise the Q, you narrow the bandwidth. In fully parametric EQs, you have
continuous bandwidth control and/or continuous Q control, which allows
you to attenuate or boost a very narrow or wide range of frequencies.
A narrow bandwidth (higher Q) has obvious benets for removing unpleasant
tones. Let’s say the snare drum in your mix has an annoying ring to it. With a
very narrow bandwidth, you can isolate this one frequency (usually around
1 kHz) and remove, or reject, it. This type of narrow band-reject lter is also
known as a notch lter. By notching out the oending frequency, you can
remove the problem without removing the instrument from the mix. A narrow
bandwidth is also useful in boosting pleasant tones of an instrument such as
the attack. Take for instance, a kick drum. A kick drum resonates somewhere
between 60 to 125 Hz, but the attack of the kick drum is much higher at 2 to
5 kHz. By setting a narrow bandwidth and boosting the attack a bit, you can
achieve a punchier kick drum without overpowering the rest of the mix.
A broad bandwidth accentuates or attenuates a larger band of frequencies. The
broad and narrow bandwidths (high and low Q) are usually used in conjunction
with one another to achieve the desired eect. Let’s look at our kick drum again.
We have a kick drum that has a great, big, low-end sound centered around 100
Hz and an attack hitting almost dead-on at 4 kHz. In this example, you would
use a broad bandwidth in the low frequency band, centered at 100 Hz, and
a narrow bandwidth boosted at 4 kHz. In this way you are accentuating the
best and downplaying everything else this particular kick drum has to oer.
Shelving EQ
A shelving EQ attenuates or boost frequencies above or below a specied cuto
point. Shelving equalizers come in two dierent varieties: high-pass and low-pass.
Low-pass shelving lters pass all frequencies below the specied
cuto frequency while attenuating all the frequencies above it. A
high-pass lter does the opposite: passing all frequencies above the
specied cut-o frequency while attenuating everything below.
Graphic EQ
The StudioLive 24.4.2 features 4 stereo, 31-band, graphic EQs that can be inserted
on a variety of buses. (See Section 5.3 for details.) A graphic EQ is a multiband
equalizer that uses sliders to adjust the amplitude for each frequency band. It
gets its name from the positions of the sliders, which graphically display the
resulting frequency-response curve. As explained in Section 5.3, the encoders
in the Fat Channel are used to make amplitude adjustments, and the meter
LEDs display the “slider” positions. The center frequency and bandwidth are
xed; the level (amplitude) for each band is the only adjustable parameter.
Graphic EQs are generally used to ne-tune the overall mix for a particular
room. For instance, if you are mixing in a “dead” room, you may want to boost
high frequencies and roll o some of the lows. If you are mixing in a “live”
room, you might need to lower the high-midrange and highest frequencies. In
general, you should not make drastic amplitude adjustments to any particular
frequency bands. Instead, make smaller, incremental adjustments over a wider
spectrum to round out your nal mix. To assist you with these adjustments, here
is an overview of which frequencies aect dierent sound characteristics:
Sub-Bass (16 Hz to 60 Hz). The lowest of these bass frequencies are felt, rather
than heard, as with freeway rumbling or an earthquake. These frequencies give
your mix a sense of power even when they only occur occasionally. However,
overemphasizing frequencies in this range will result in a muddy mix.
Bass (60 Hz to 250 Hz). Because this range contains the fundamental notes
of the rhythm section, any EQ changes will aect the balance of your mix,
making it fat or thin. Too much emphasis will make for a boomy mix.
Low Mids (250 Hz to 2 kHz). In general, you will want to emphasize the lower
portion of this range and deemphasize the upper portion. Boosting the range
from 250 Hz to 500 Hz will accent ambience in the studio and will add clarity to
bass and lower frequency instruments. The range between 500 Hz and 2 kHz
can make midrange instruments (guitar, snare, saxophone, etc.) “honky,” and too
8.3 Equalizers Equalizers 8.3