A mic can have different pickup patterns. What do I mean by that? I mean, a mic does not only pickup the sound that is in the immediate front of it, it may also pick up sounds behind, or to the sides of the microphone.
Here are the different kinds of patterns. Understand them when
looking for a mic to buy and your intended application.
Bi-Directional
This is also called figure-8. It picks up sound in front and rear of the diaphragm, but does not pickup sounds from the sides. These types of mics are often used above an instrument or used for "stereo" recording in an M-S matrix technique.
Cardioid
This is the most popular mic pattern. Basically, it looks like a heart. It picks up sound where the mic is pointed at, but some of the sounds from the rear are also picked up, though not as much. Usually about -10 to -30dB lower.
Just be careful though, because the shape of the cardioid isn't fixed. It varies it's shape depending on the frequency. So it could be sensitive for some frequencies and not for others. This can be used for good use because the mic imparts some "coloration" to the sound.
Sample Cardioid pickup pattern of an
MXL 604 mic.
This type of mic is also good for "proximity effect." i.e. the closer you get to the mic, the lower frequencies are hyped up, adding "body" and fullness to the sound. However, sometimes it's too much. So you can do 2 things... one, move the mic farther away, (or you move farther away), or if the mic has a built-in low-pass filter, activate that. (if your preamp has a low-cut filter, you can also activate that).
Omni-DirectionalFrom the word "omni", this mic responds as evenly as possible from all directions.
Stereo Mics
Nowadays, you can buy stereo mics. These microphones have 2 diagphragms in the same body, usually, they're angled toe-in. The capsules are matched for even frequency response for both Left and Right channels. Now... there are 2 kinds of stereo mics.. the cheap ones that are mainly used for videocam cameras (usually, 1/8" jack), and the professional ones complete with XLR jacks.
Rode NT4 Stereo Condenser Microphone"ALL OF THE ABOVE" Pattern
Due to great advances in technology, there are now mics that are "all of the above" (except stereo). A single mic can be switched to omni, cardioid or bi-directional by the simple flick of a switch. If you're on a budget, these mics are a good buy since it's like buying 3 mics for the price of one.
Rode NT2-A microphone featuring switchable patterns, low cut filter, and pads.