Groove Tubes: Basic Miking Concepts
Microphone placement is an area in which art meets
science. Microphone choice and placement is somewhat subjective,
much in the same way that choosing a guitar and amp is a matter
of personal preference. Furthermore, each situation brings a difference
confluence of performer, sound space, recording equipment and creative
forces. The question is not one of the right or wrong mic or technique,
but simply one of what works best in each unique situation. Nonetheless,
it’s best to know the “rules” in order to break
them with the greatest success. Here, then, are some generalizations
to consider. Note that since condenser mics are used in the vast
majority of studio situations, all of the following application
tips apply to condenser mics.
All recording spaces have a unique ambient quality that determines
how sound from the source will be reflected. Those reflections are
candidates for being picked up in the microphone(s) along with the
direct sound from the source. The choice of microphone, pattern
and placement depends in part on the balance you wish to strike
between the sound source and the ambient characteristic of the recording
space. Another critical consideration is isolation from other sound
sources. In many ways, it all comes down to envisioning the sonic
focus you want the mic to have.
(Microphones potentially receive
reflections from the room and other
objects as well as sounds emanating directly from the source.)
Close-Miking vs. Distance-Miking Techniques
In general, close-miking techniques (where the microphone is very
close to the sound source) are used in conjunction with a cardioid
or super-cardioid to focus the pickup pattern on the source while
simultaneously avoiding any significant influence from the surrounding
space. Close-miking with cardioids (or super-cardioids for extreme
situations) is also very useful in isolating the sound source from
other performers. Note also that the closer the mic is to the source,
the more prevalent the performance by-products (such as breath,
fret noise, snare rattles and piano hammers) will be. With close-miking,
the illusion of space is likely to be added electronically in post-production
via reverb and/or other forms of time-delay devices.
Placing any mic at a greater distance from the source will add more
of the room reflections. Distance-miking refers to microphone placement
intended to incorporate at least some room reflections. An omni
pattern opens up the recording to incorporate the full ambience
of a room. Regardless of the pattern, a proper balance must be found
in order to maintain the presence of the source while incorporating
surrounding ambience. When enough mics are available, engineers
often employ both close- and distance-miking techniques simultaneously
in order to control the balance of direct and room sound.
The further the microphone is from the source, the less sensitive
it is to the sound emanating from that source. This falloff is not
linear. Microphone sensitivity exhibits the law of inverse squares—i.e.
sound power reaching the microphone varies inversely as the square
of the distance from the source. For example, the typical mic is
exposed to only one-quarter the sound power at twice the distance
from the source. (You can think of this as the aural equivalent
of the exponential falloff in light as you get further away from
a light bulb.)
(Sound power falls off exponentially
with distance according to the law of inverse squares.)
Recall also that large-diaphragm cardioid microphones
exhibit a proximity effect where the low-mid frequencies increase
as the distance between the source and mic decreases. (The proximity
effect is not a big issue with omni patterns or medium-sized capsules
of any pattern.) With large diaphragms, the placement of the mic
affects volume, room ambiance and tonality.
Large Capsules vs. Medium Capsules
You can achieve excellent results in most situations
using either medium- or large-capsule Groove Tubes mics. This is
at least in part due to the fact that Groove Tubes medium-capsule
models like the GT33 and GT44 have diaphragms the size of some manufacturers’
“large” capsules.
That said, there are some practical differences.
As a rule of thumb, the large-capsule mics like the GT67, GT57,
Model 1B and Model 1B FET will have more sensitivity in the low
end than the medium capsules simply because the diaphragms are larger.
As previously mentioned, they also exhibit more proximity effect
in cardioid patterns (which can be positive or negative depending
on the circumstances). Furthermore, they take up more physical space
so they are less adaptable in tight situations. Conversely, medium
capsules tend to exhibit flatter frequency response regardless of
distance and are more flexible when space is a consideration. You’ll
eventually want to have both large- and medium-capsule models in
your mic locker.
Next month we’ll take a closer look at how
the recording environment itself influences open-mic recordings.
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