This type of microphone will pick up sound evenly from all directions, hence the omni- prefix (they are sometimes called non-directional). For this reason, omnis should be used only when recording very close to the source. It is generally felt that omnis offer the best sound as compared to directional mics, and top omnis are often less expensive than top directional mics.
For an audience application, omnis are generally only used for fob (upfront) recordings, since they tend to pick up too much audience noise when used at too great a distance. Another common audience application is to use an omni/shotgun mix from further back in the hall. The shotguns are used to pick up the direct sound from the sound system while the omnis provide ambient information. The reasoning behind this method is to give “presence” to the mix, which would be lacking in a shotgun-only recording.
When using a spaced omni setup (several inches to several feet between mics) in quiet venues, distance is less important a factor; quality recordings can be made even far from the source. For binaural recordings (with the omnidirectional microphones mounted near your ears and the recording played back over headphones), closeness to the source is only a minor factor in achieving a quality recording.
This type of microphone is slightly more directional than omnis. Much of the sound coming from behind the microphone is not picked up. There is also a small amount of side rejection as well.
Cardioids are often used as vocal mics since they will not pick up most of the other noise onstage coming from the amps, monitors, etc. For a Dead-show-type application, proximity to the sound source is important, though not quite as critical as with omnis.
Like omnis, you will get the best results when used upfront. Some people use cardioids from further back, but audience noise becomes more of a problem the farther back you go. If you plan to use cardioids from a large distance, the best results are usually obtained when the mics are elevated as far as possible above the audience in order to minimize crowd noise on the recording. Cardioids usually work well in a small club setting and also outdoor amphi-theatres, where the crowd noise tends to be more attenuated than on indoor audience recordings due to the lack of reflective surfaces (i.e. side walls and ceilings). A cardioid which has a 20-20000 Hz frequency resonse will generally be less expensive than a comparable hypercardioid or shotgun.
This type of microphone is more directional than standard cardioids but less directional than shotguns. Hypercardioids are *not* shotguns. They can be thought of as “short shotguns.” They have more side rejection than cardioids but not as much as shotguns. Excellent results can be obtained from far back as well as upfront. They also work quite well in small clubs. Hypercardioids are generally the least common of the polar patterns and you can expect to pay a tidy sum for a good pair.
This type of microphone is the most directional of the four. Shotguns have the most side rejection and thus are well suited for recording at a large distance. Shotguns are the microphone of choice in the tapers’ section at Grateful Dead shows. Shotguns tend to have a number of drawbacks, however. The less expensive shotguns will not have very good frequency response, especially in the lower octaves. For this reason, lower-end shotguns are often described as “tinny” or “hollow” sounding. Also, the drastic side rejection of a shotgun often results in recordings with a lack of “presence.” Expect to pay a fairly large sum to get a shotgun with 20-20000 Hz performance. Because of their large size, shotguns are not usually used upfront. Directionality is useful for increasing the ratio of direct sound (from the stage and P.A. system) to reverberant and ambient sound (from the rest of the room). This becomes more critical as the distance from mic to stage is increased. Generally, one must pay more money for a shotgun in order to get as good sonic characteristics versus a less directional mic.
In contrast to omni’s and cardiods, microphone placement is very critical with shotgun capsules, which some believe is more often the reason behind the “tinny, hollow” sound than the technical qualities of the microphones themselves. These mics are very directional, and you really have to consider the fact that they are recording where you point them — unlike omnis which record the sound where they are located.