Omni-directional Microphones pick up sound equally in all directions around the microphone. These are usually found as Lapel microphones and some handheld microphones. The lines shown on the picture to the right are a representation of the polar pattern of the microphone (remember this is a two dimensional representation of what is a three dimensional pattern) An omnidirectional mic has a circular (spherical) pattern.

Bi-directional Microphones
These pick up sound mainly in two directions, in front and behind the microphone diaphragm. They are generally used in studio situations, such as radio interview studios. This is Represented by a figure of eight polar pattern.

Uni-directional (Cardoid) Microphones
These are called cardoid because the representation of their polar pattern (shown to the right) looks heart shaped. They pick up sound primarily in one direction, with far less sound being picked up as one goes “off mic” to the side and behind the microphone. With a handheld cardoid microphone it is important to make sure it is always pointing at the mouth of
the person speaking. The two variations on this type - Hyper-cardoid and Super-cardoid - have much narrower pick up patterns and are used for shotgun microphones. The pointing of these is therefore much more critical than with a handheld cardoid microphone.

Shotgun Microphones
This is the way mainstream producers get good sound. However good quality shotgun microphones are expensive, not to mention their accessories such as the mounting cage, boom pole and fluffy wind shield - which can be as expensive as the microphone itself, and the portable audio mixer to run it through.