Recording - May 2015 - 47

3
starting pistol.) After recording the impulse, software translates
its behavior into a frequency response curve.
The last way to produce a frequency response chart is timeless: Louie, the graphic designer in Marketing, draws it freehand or on a computer.
If you see a mic frequency response curve that looks suspiciously smooth, suspect the presence of Louie; real microphones have bumpy measured responses that look more like
Figure 3 than Figures 1 and 2. (It's also possible to fudge the
swept-signal and impulse response measurements to produce
artificially smooth charts.) Happily, unless the bumps are large
ones, you don't usually hear them; as a result, a case can be
made that the Louie curves are valid-if he has good ears.
You can think of a frequency response curve as a coloration
the mic imposes on every sound source it records. The recording engineer chooses a mic with a frequency response that
makes the instrument being recorded sound like itself in the
recording monitors-or sound the way he or she wants it to
sound (not always the same thing). It's that choice that first
defines the art/science of recording; Once you have a good
player with a good instrument, then mic choice, more than
anything else, will influence the raw sound the engineer works
with. (Room acoustics run a close second.)

Full frontal microphones, etc.
I want to talk about a couple of unstated assumptions that
go with mics' frequency response charts. The first assumption
is that the graph is talking about what happens when the

You can think of a frequency response curve as a coloration the mic imposes on
every sound source it records. The recording engineer chooses a mic with a
frequency response that makes the instrument being recorded sound like itself...
or sound the way he or she wants it to (not always the same thing).
sound source is directly in front of the microphone-at 0°, in
engineer talk. As you'd guess from the discussion last month
of how pickup patterns vary with frequency, what happens onaxis is different from what happens when the sound source is
90° off axis-and what happens when the source is behind
the microphone (180°) is way different.
Sometimes a manufacturer will be extra nice and give you
graphs of a mic's off-axis performance. An example is Figure
4, a response chart for Electro-Voice's RE20 mic-ignore the
dashed lines for the moment.
Up close and personal
The other unstated assumption in reading a mic's frequency
response chart is that what's depicted applies to a sound source
far away from the microphone. Many mics have something
called proximity effect (PE); when they're used close to a source,
the response in the bass increases, as shown in Figure 5. The
lower trace shows the conventional response, measured with the
source at a distance (usually a meter or further); the upper trace
shows the same microphone's response when the source is only
1cm away-very close. As you see, there's a big rise in the bass.
Have you ever seen an old film or video of Frank Sinatra performing with a handheld mic? If so, you can watch him moving the
mic in and out from his mouth as he goes from line to line, word to
word. Partly he was compensating for loudness changes, of course:

moving out on loud notes, in on soft ones. But he was also working the
mic's frequency response; when the mic was closer, he got a richer,
bassier sound that put more mellowness onto his soft tones. Artists from
Sinatra's era were masters at using proximity effect for controlling tone.
Proximity effect happens with most directional mics; the more
directional, the more it happens. Here's the rundown:
Omnidirectional-no PE; Cardioid-some PE; Hypercardioid-more
PE; Bidirectional (figure-8)-maximum PE.
I said most directional mics; there are a few exceptions. Some
Electro-Voice cardioid and hypercardioid microphones show little
or no proximity effect; E-V calls these "Variable-D®" microphones,
because they sound pretty much the same at varying distances.
(Tonally the same, that is; of course the volume varies with distance.) This makes them useful for radio announcers (who sometimes bounce around), and E-V's Variable-D RE20 has become the
standard announce mic for many radio stations and networks.
Among the mics with little proximity effect are E-V's RE15, RE16
(an RE15 with a pop filter) and RE20. (Shure's SM53 and SM54
had similar properties, but they're long discontinued.) Some largediaphragm condenser mics also show very little proximity effect,
for a different reason: at low frequencies, their cardioid or hypercardioid pickup patterns turn omnidirectional, and omni mics
have no proximity effect. Neumann's U 87 is a good example;
that's one reason it's held its place over the years as a "go-to"
microphone for studio vocals.
RECORDING May 2015

Recording - May 2015

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