9--Pick Up Patterns
One of the more important things to know about a microphone is the area around the microphone that it will "pick up" versus the area it will ignore. Some pick up sound from all angles, others favor sound from just one angle---the front for example.These directional characteristics are classified as Omnidirectional, Bidirectional, Unidirectional or Cardioid. Just as a frequency graph will provide a useful indication of the microphones frequency response, a "polar" chart will provide a useful visual indication of a microphone's directional characteristic. A polar chart is if you are looking down on the mic and seeing what "pattern" there is to the sound it will accept.
Omnidirectional Microphone Pattern
An Omnidirectional pattern or "Omni" mic will pick up sound equally well from all directions above and below, front and back. Omnidirectional microphones usually have a very flat response. This is ideal when you want to record everything in the room or you do not want the sound to change with location of the source. The most common application for an Omni is those "on location" TV interviews you see on the news. They are very useful where relatively inexperienced people are talking into and using the mic. Since the sound is picked up equally in all directions, you do not need to point the mic at one thing to "hear" it. There is no proximity effect with an Omni so you do not have bass boost changing the sound of the source.
The Omni mic is not commonly used in live sound or recording for the same reason it works in TV news---it hears everything. You have no option of avoiding unwanted sounds and isolating the sound you actually want. If you are trying to record a single drum of a drum set, it cannot be done with an Omni. You need a mic that will isolate just the drum you want from the set of many drums.
In live sound, an Omnidirectional microphone is often a bad choice because it will pick up various reflections of the sound you want from nearby walls, floors, ceilings, etc. An Omni can produce a very hollow sound on a mic stand on stage, where the sound from a singer hits the floor and bounces back up into the same mic they are singing into, canceling some of the sound you want. In live sound applications, you are less likely to use an Omni because you have a much greater risk of feedback when the mic picks up the sound from the speakers as well as the vocals! Omnis are most often seen as condensers in the recording of orchestras in excellent sounding rooms.
Bi-Directional Pattern
Bi-directional pattern, also called a figure eight pattern, is most common with ribbon microphones which are inherently "front and back" mics. Some studio condenser mics still offer figure eight patterns. In the early days of radio, it was used for capturing the performer and a live audience simultaneously, or two people sitting facing each other at table. Not useful for live sound, this pattern is most useful in advanced recording techniques called Mid/Side. There is no proximity effect with a bi-directional microphone.
Cardioid or Unidirectional Pattern
A Cardioid microphone is a microphone that picks up mostly from the front. Its pattern looks like a heart on a polar response chart, hence the name cardioid. The cardioid mic will focus its pick up pattern on things that arrive at the front of the mic, so you can point it at the sound you want and away from sound you don't want. This is the most popular pattern for live sound (it ignores the floor monitors and out front PA system) for it has greater "gain before feedback". This pattern allows you to eliminate the problems encountered with the Omni pattern because it can be pointed away from sounds you do not want. It is also the most important microphone for recording, for a user can focus the mic on just the instrument desired. It can also make a recording in a bad room better, because it "hears" less of the room and more of what is right in front of it.
Cardioids all have some form of proximity effect, which is an unavoidable by-product of eliminating sound from the rear. With careful application, this proximity effect can be used to your advantage.
Super Cardioid or HyperCardioid Pattern
The Super and Hyper Cardioid pick up patterns have higher directionality and rejection of sound coming from the sides than Cardioids, but slightly more pick up of bass from the rear. They are very useful in isolating the desired sounds from the front and rejecting unwanted and ambient sounds from the rear and side. The caveat here is that the "acceptance angle" or pick up area is very small and the performer must stay directly "on axis" or directly in front of the mic to be picked up. Side to side movements can put a performer in and out of the pattern very quickly and cause significant problems for the sound system operator. The pattern is most useful in stable, non moving sources for live sound.
Specialty Patterns
The Shotgun mic is a very hyper cardioid that has a very narrow pattern but has greater "reach", so the source can be further away than a normal cardioid or hyper cardioid. This mic can work a source that's 3 feet way. This mic is best used on location video, TV talk shows hung from a big boom and location movie work. It is used primarily to isolate sound in higher noise (high ambient noise) environments. The Parabolic mic has a very narrow, pencil like far reaching pattern and is best applied on football field sidelines where the microphone will be very distant from the sound source (the football players). This mic works on sources over 30 feet way. This mic has very poor sound quality for you are using a dish to focus the sound. It is not used for any high fidelity applications.
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