Recording - December 2015 - 40

By Paul J. Stamler

 
Let's get right down to it: Why did I call this article "Atmospheres and Control" when it's
really about equalizers? Because atmosphere is what we're talking about. An equalizer (or
EQ) can change bright sounds to dull, bring out or de-emphasize vocal consonants, tame a
too-honky sax or a screechy violin. EQ can move an instrument closer to the listener, or farther
away. It can, at least partially, compensate for a poor match between mic and instrument,
eliminating valve clicks, pick noise or vocal sibilance. (We agreed a while ago that the voice
is an instrument; most singers will agree.)
There are also things an EQ can't do. One persistent urban legend of audio is that an equalizer can make any microphone sound like any other. Well, it can't; there's no amount of EQ
that can make a Shure SM57 sound like a Neumann U 47, or vice versa. The differences
between microphones aren't all frequency response; there are also what engineers call nonlinearities, which have as much to do with what a mic actually sounds like as the (frontal, medium distance) frequency response curve that gets published.
On the other hand, some engineers avoid EQ altogether, preferring to shape their sound
entirely by mic choice and placement; often you'll hear EQ referred to as a "Band-Aid". But,
as any ambulance driver will tell you, sometimes Band-Aids save lives. And sometimes a little
EQ, applied sparingly, can make the difference between almost there and there.

Figure 1

There's something of a cultural difference between seasoned recording engineers and newbies; the experienced folks tend to use EQ conservatively, while people new to the business
tend to slather on EQ boosts like ketchup. That's useful for a special effect, like the drastic highfrequency boost Geoff Emerick applied to the drums in the Beatles' "Tomorrow Never Knows".
But you wouldn't want ketchup on everything (at least I hope not), and a nuanced approach
to EQ makes for better recordings.
End of sermon. Let's talk about the EQ you'll find in a studio. Note that I won't make big
distinctions between hardware and software EQ in this article; the reason is that in my opinion there isn't much difference between them when you compare the finished results. Mostly.
Your mileage is welcome to vary. (And also see below.)
Off the shelf
An equalizer is a tone control with a college education. So I'll begin with the type of equalizer that's closest to the tone controls found on consumer listening equipment, the shelving
equalizer. (Tone controls on guitar and bass amps form a category all their own, which I won't
cover here.)




Shelving EQs paint with a broad brush;
low frequency (LF) controls, better known as
bass controls, turn up or down everything
below a certain frequency, while high frequency (HF) controls, better known as treble
controls, do the same for everything above a
certain frequency. Take a look at Figure 1,
which shows the effects of some typical bass
and treble shelving equalizers, as found on
many consoles (including the virtual consoles
we call DAWs); I drew multiple curves representing different values of boost and cut.
You'll see that the bass control cranks up or
down everything below 200 Hz; the treble
does likewise for everything above 2 kHz. In
this sort of equalizer, these are known as the
hinge frequencies or inflection points. On
some consoles and processors (and many
DAWs), you can choose the inflection points.
A few British consoles offer "tilt" controls;
they turn the bass down and the treble up an
equal amount, or vice versa. This idea isn't
well known in the USA, and I haven't seen a
software version, though it'd be easy enough
to do. [Fortunately, I have: check out the marvelous niveau filter from elysia, which happens to be free!-MM]
A variation on the shelving EQ is called
the variable inflection equalizer. See Figure
2; I've only drawn the boost curves, to make
it easier to see what's going on. In this
design, the frequency at which the response
reaches the shelving level is what's specified;
as you turn, say, the bass control up or
down, the effect extends further into the
midrange. These days I see this mostly in software equalizers, such as the shelving EQ in
Adobe Audition's "Parametric EQ" window.
("Parametric"? What's that? Keep reading.)
A sharper scalpel
For most of the history of recording, the
only equalizers found in consoles were
shelving, and typical studios didn't have
many of them. When Bill Putnam built his
famous consoles for Universal Studios, the
shelving EQs he built into all 12 channels
were considered the height of luxury. The
REDD 47 console that EMI designed for
their Abbey Road studios likewise had a
shelving EQ on every channel, which their
engineers thought was the cat's meow
(well, the bee's knees in the UK).

Table of Contents for the Digital Edition of Recording - December 2015