Recording - May 2015 - 48

Some mics include a switchable bass
rolloff to compensate for proximity effect.
Go back to Figure 4-remember those
dashed lines? The RE20 is designed to
minimize proximity effect, but it does
have some, and there's a switchable bass
rolloff to compensate for it. The dashed
lines show the mic's response with its bass
rolloff switched in.
Other mics have no bass rolloff switch;
many mic preamps, including those in
consoles, include a bass rolloff (often
called a highpass filter). It's also possible
to add the rolloff during mixdown, of
course; most DAW software includes filtering. I've found that a filter which rolls
off frequencies downwards of 100 Hz
compensates well for proximity effect
most of the time.
Harmonic convergence

5

Over the years, as professional
microphones
have
evolved in the marketplace,
many of them have converged
on a frequency response that
isn't flat, but looks something
like Figure 6, with a small (or, in
some mics, not so small) rise up
top. For the record, Figure 6 shows the
frontal frequency response of a Neumann
U 87, with its pickup pattern set to cardioid.
Sometimes this was making a virtue of
necessity. If you stretch a thin membrane
over a circular rim, which is how condenser mic capsules are made, you get
something that looks and acts like a
drum. In fact, the breakthrough which
made possible the first practical condenser mic, back in 1916, came when
the inventor found a way to push that
drumhead resonance out of the midrange
and into the treble, while damping it
down to a relatively manageable bump.
(Other physical effects contribute, but if I
spent time on them, this would turn into a
weighty tome.)
Designers have lived with that drumhead resonance ever since. Some mics,
usually cheap, don't damp it much; they
have relatively sharp peaks in the treble
48

RECORDING May 2015

that sound shrieky or sibilant. Better mics
damp it down to relatively benign levels,
and a very few manage to achieve
response that's pretty flat, on- and offaxis. One reason most ribbon mics sound
different from most condenser mics is that
they lack this drumhead resonance.
A matter of tastes
The reasons for this convergence are
book-length complicated. When electrical
recording of sound was introduced in the
1920s, the bump in treble response
helped compensate for lack of treble
response in the record/reproduce chain.
Using microphones with responses like
Figure 6 also helped when mics were
placed far from sound sources; the rise in
the treble compensated for the treble
soak-up of the atmosphere.

the 1940s, and we've learned over the
years that this is what recordings are supposed to sound like. Flat mics are often the
main mics for classical recordings, but
mics with responses like Figure 6 are the
norm for most non-classical recordings;
we've come to accept and crave their
slight forwardness. It's something of a circular process: almost everyone uses them,
because almost everyone else uses them.
In the introduction to this series, I mentioned that I usually aim for a natural
sound in my recordings-an approach
that comes closer to documentary photography than the current practice of
assembling a sonic collage from separately recorded bits and pieces.
So does that mean that I always use
microphones with flat responses? Umm,
no. I also mentioned that sometimes it
takes a non-flat response to sound "natural", and for this recording I used one flat
mic, two almost-flat mics, a couple that

Many mics have something called proximity effect;
when they're used close to a source,
the response in the bass increases.
6

had responses close to the
response in Figure 6, and one
wildly unflat mic.
Off the charts
After spending so much ink
and paper talking about frequency response charts, I need to note

Well, except for classical recordings,
we don't mike things from far away very
often these days (except for overhead
mics on drums), and today's record/
reproduce chain isn't deficient in treble
response; in fact, the treble is occasionally excessive. So why do mics with Figure
6 response remain popular?
For one thing, they sound close; that
treble bump makes most instruments and
especially voices sound prominent and
"present". It helps voices stand out from
an instrumental background, and the treble bump helps emphasize consonants
for better intelligibility. (Sometimes, unfortunately, this can translate into excessive
sibilance. I'll talk a little about that next
month.)
But I think one reason we like the Figure
6 response is that we've learned to like it.
Mics with responses like Figure 6 have
been nearly ubiquitous in pro studios
since Neumann introduced the U 47 in

7

that they don't tell the whole story, though
they can provide a useful starting point
when you're picking mics for a session.
The thing is, there are some aspects of a
microphone's sound that just don't show up
on frequency response charts. Go back to
Figure 6; it indicates that this mic will
sound just a bit bright and forward, which
might (if you're not careful with placement)
emphasize sibilance in a singer's voice
and pick/fret noise on an acoustic guitar.
What the chart doesn't tell you is that this
particular microphone, the Neumann U 87,
has a very specific sound when it's used on
plucked instruments, a sound best described
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