BASICS OF MICROPHONES

How microphones work

Microphones convert sound waves into electrical audio signals.
To do this they have a thin sheet of material in them called the
diaphragm. When the sound vibrations in the air reach the diaphragm,
they cause it to vibrate. This causes the electrical current in the
microphone to change.  Microphones are usually classified by the method
by which the diaphragm works.

Types of Microphones

Dynamic Microphones

Dynamic microphones use moving-coils. This means a diaphragm of
thin plastic is attached directly to a coil of wire. The coil has
a magnet surrounding it in its middle. As the diaphragm vibrates,
the coil vibrates as well, this causes a varying amount of current to
pass through the coil. This is converted to your audio signal.

Condenser Microphones

In condenser microphones, an electrical charge is present in the
diaphragm or in a plate behind the diaphragm. As the diaphragm vibrates,
the distance between the diaphragm and he plate changes, changing the
electrical capacitance of the diaphragm and the plate. This changing 
capacitance causes a change in the electrical current. Again, this
change is your audio signal.

Phantom Power

Condenser microphones need a power source to charge the capacitor.
Three methods are typically used. A battery can be inserted inside
the microphone, a permanent charge can be placed on the diaphragm or
plate, or phantom power can be used.  Phantom power is power supplied
through the ground cable of an XLR cable. This power is supplied by a
battery pack when taping live shows.

Pick Up Patterns

Omnidirectional

        These microphones pick up sound evenly from all
        directions.  As a result, in audience applications,
        they are best used only for FOB (Front Of Board) recordings,
        since they pick up too much audience noise when used
        at a distance.

Cardioid

        These microphones are more directional than omnis.
        Most of the sound from behind the microphone is blocked out and 
        there is also some side rejection.  If you use cardioids from
        the tapers' section at shows, the best results can usually be 
        obtained when you elevate the mics  as far as you can above
        the audience.  This will help minimize crowd noise on the recording.
        I use cardoids myself, and am very pleased with the results.
        I raise them to about 10 feet, so crowd noise is minimized.

Hypercardioid

        These microphones are more directional than cardioids but less
        directional than shotguns.  Typically, hypercardoids offer more
        side rejection than cardioids but not as much as shotguns.  

Shotgun

        These microphones are the most directional. Shotguns offer the 
        highest degree of side rejection.  Shotguns have a number of
        drawbacks, however.  Less expensive shotguns have poor frequency
        response, especially in the lower octaves. The drastic side
        rejection of shotguns result in recordings with a lack of
        "presence."  As a result, they are not desireable as main
        microphones for recording live, but can be used as spot
        microphones when mixed with cardoids or hpercardoids.

Techniques

X-Y Techniques for Hypercardiods & Cardioids

The most common technique is the x-y cardioid and hypercardioid.
The microphone pair is setup at an angle of 60 to 120 degrees.
The angle determines the width of the stereo image, the amount of
reverberation and the bass response. I use an angle of about 110 degrees
when taoing outdoor shows, and most use an angle of 90 degrees when
taping indoors.

Binaural Technique

This technique uses omnidirectional microphones worn on your head.  This
reproduces sound most like you hear it, but must be listened to over
headphones to be fully appreciated.  Most often, the microphoness used
in binaural recording are small (about the size of a jellybean).
Microphones can be purchased that are worn inside the ear, as well.