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The Magic of Microphones
By Roberto Luz
Though it's rapidly becoming something of a lost art, the selection and use of good quality microphones will never be completely abandoned as long as there are acoustic instruments and human voices to be recorded. Even with the newer totally electronic styles basic microphone techniques are still an important part of the lives of most studio technicians.
Sampling, for example; some of the most creative samplists around do almost all of their work with a portable DAT machine and good quality mic. And, of course, if you're going to use any kind of vocals other than sampled ones, you're likely to find yourself in need of a reasonable mic and some knowledge of how to set it up.
Since there is an unbreakable link between the sound you hear and the final sound that ends up on your CD, the importance of microphone design cannot be overstated. Anyone working in a studio needs to understand microphone technology and have a reasonable knowledge of the range of the mics that are currently available.
There's nothing particularly complex about mic technology and, even though there is an endless range of
models available from each manufacturer, for most practical purposes these break down into three or four
basic types, with perhaps four different types of pickup responses - and this last characteristic is the
one we'll look at first.
The pickup characteristic of a microphone refers to its ability to respond to sound coming from different directions. Microphones react in different ways: some pick up more or less equally in all directions; others respond to sound from some directions, but are virtually 'deaf' to others. This can be put to good use when it you're choosing the correct mic for the job.
For instance, when miking a vocalist performing on his or her own, it would be preferable to use a microphone which picked up only in one direction, limiting the possibility of noise entering the mic from the rear or the sides.
This would also be of use in certain drum miking applications; where, for example, the sound of the snare drum needs to be picked up without spillage from other drums and cymbals.
By contrast, if we're using a single overhead microphone to capture the 'live' sound of a drum kit, we obviously wouldn't want to restrict the pickup area of the microphone to a narrow band. A microphone responding equally to sound from all directions would be called for.
The two types of microphones highlighted here are generally referred to as unidirectional (picking up sound in only one direction) and omni directional (picking up equally in all directions).
There are other configurations of mics for different technical uses, but, for the home recorder, you need at least a fair sampling of these two basic types.
For a drum kit you would use a combination: small unidirectional (or cardioid) mikes for the different drums, and an omni directional mic (or two) placed above the whole kit to get the ambient sound of the drums.
The word 'cardioid' in microphone terminology is used to describe the polar response of unidirectional microphones. A regular cordioid pick-up area is roughly heart-shaped; this means it isn't exactly 'one directional', but it's very close
Some common microphone pick-up response patterns:
A - Omni-Directional;
B - Cardioid;
C - Hyper-Cardioid;
D - Figure of Eight
A cardioid design would normally be the preferred choice for miking instrument amplifiers
Hyper cardioid mics are super pinpoint mics.
Figure eight mics are used where a mic is placed within a sound field (rather than simply in front of it).
A 'figure-of-eight' type will give you a fuller, more rounded sound when placed in the middle of everything.
Now let's look more closely at the most common types of mics currently available...
The most widely-used type of mic - by a considerable margin - is the dynamic or moving-coil mic, which uses a lightweight circular diaphragm attached to a fine coil of wire to pick up the sounds.
Dynamic mics have several distinct advantages over other types; they are relatively cheap to manufacture and pretty hurky. This makes them useful for live work as well as in the studio, and it also means that dynamic mics are especially suitable for use with percussion instruments. A good example of this mic is a Shure SM58
A more recent innovation, the capacitor (or condenser) mic works on the principal of varying
electrical capacitance. Simply put: the capacitance formed by two metal plates - one fixed and
static, the other thin and flexible - varies in relation to the distance between the two plates.
This distance fluctuates as a result of sound waves exerting pressure on the flexible plate or
'diaphragm'. Because a voltage must be applied to the plates, capacitor microphones require a
power supply. This usually takes the form of a 48V supply derived from a mixing desk or other
amplification system, and is referred to as 'phantom power'.
Capacitor microphones tend to be more expensive than dynamics. However, the improvement in
performance is considerable. Because the diaphragm can be made so thin, much less energy is
required to move it. This means that sensitivity is increased. Capacitor microphones are
used wherever serious recording work is carried out, but are sensitive to rough handling and
so are not generally suitable for live work. In most applications, they reproduce sound much
more accurately than dynamic mics do, and this makes them particularly suitable for 'difficult'
instruments such as cymbals, which require good high frequency response and speedy transient
response to cope with the high harmonic content of the sound.
Often, dynamic mics are chosen because their sound, though colored, is actually flattering to a particular instrument. On the other hand, their accuracy does mean that capacitor mics can be used across a wide range of applications, so they make an excellent choice in the studio, where they can be put to work on anything from vocals to acoustic guitars to pianos.
Capacitor mics are more expensive, but seem to be getting cheaper all the time.
A good combination of the different types of mic is essential for doing the magic that you
are looking for in the studio.