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Amateur Recording
Part 7. Microphones

Anyone first getting into recording will quickly realize that microphones are where it's at. It follows the old adage: garbage in, garbage out. Since the microphone is the first mechanism a sound hits on its way into the recorder, it makes sense that no matter how good your recording deck is, if you have a bad microphone, your going to get a bad recording. In this way, the microphone is comparable to a photographer's lense. In addition to effecting the quality of the image a photographer captures, each lense has different attributes in terms of depth-of-field, aperture, field-of-view, etc. Likewise, different microphones will also offer different recording characteristics that affect the tone and range of the recording. And, just as the photographer has a wide range of lenses to chose from, there are a wide range of microphones. This section is an attempt to identify many of the different types of microphones out there and what characteristics they share.

Transducer Types

A transducer, simply put, is a device that translates a signal from one medium to another. A microphone transducer, for example, translates kinetic energy (oscillating air particles) into an electrical signal (oscillating voltage). There are two main categories of microphone transducers: dynamic and condenser. A dynamic microphone contains a diaphragm that is connected either to a voice coil or a piezoelectric crystal. As the diaphragm is compressed by incoming sound waves, it generates an electric current, which is the signal that gets recorded. Dynamic microphones require no external electric power, but typically require much louder sound sources and tend to color the sound they are recording (often in beneficial ways).

Modern condenser mics use an electret design in which an external power source is used to create a far more accurate recording of the original sound source. This external power may come from a battery, power supply, or from phantom power provided by any of several mic preamps on the market. While condenser mics can create a more accurate recording the original performance, this includes accurately recording all of the noise in the room, as well. In many cases, condenser mics tend to pick up excess high-end frequencies, resulting in over-exaggerated esses and overly bright recordings. On the other hand, condenser mics are ideal for recording low volume sound sources that are simply not loud enough for a dynamic mic to capture. Of course, this also means that condenser mics will tend to be more sensitive to loud sources, often resulting in distortion. Dynamic mics, in general, do not suffer from this problem.

Microphone Response Patterns

Microphones come with a diverse variety of response patterns. The polar response pattern refers to how the microphone picks up sounds from different angles relative to the microphone. This is somewhat analogous to standard vs. wide-angle vs. telephoto camera lenses. The following are some of the more common microphone response patterns: omnidirectional, cardioid, hypercardioid, and shotgun.


Microphone response patterns, or "polar patterns."

Omnidirectional microphones, as the name implies, will pick up sound evenly from all directions. These mics tend to be somewhat less expensive than their directional counterparts, and some would argue that they provide better sound. However, since omnis essentially pick up everything, there are relatively few applications that they are well suited for. Typically, omnis are used in cases where the microphone can be placed very close to the intended source, or when the recording environment is very quiet such that there is little or no interference with the sound source. An omni is sometimes used in conjunction with a pair shotgun microphones to record live performances. In such a scenario, the shotguns are focused on the performance while the omni is used to pick up the ambient information, giving a greater sense of the space in which the recording was being made.

Cardioid microphones respond to a heart-shaped (thus the name) area around the microphone. In other words, the microphone picks up very little sound from directly behind it, but the response increases as you come around to the front. This type of microphone is commonly used for recording vocals due to its ability to avoid picking up other sound sources on stage such as amps and monitors. The key to effective use of cardioid mics is to realize that it will pick up anything in front of the microphone. This means that recording at a live show will often work fine as long as there isn't too much audience in front of you.

Hypercardioid microphones are essentially like narrower, more directed cardioid mics. They essentially have more side rejection than cardioids, but not as much as the very directional shotgun microphones. While some would argue that hypercardioid mics are among the most flexible of those discussed here, they also tend to be among the most expensive.

Shotgun microphones are, by far, the most directional and often among the most expensive. Essentially, shotgun mics are designed to be very focused, demonstrating a great deal of side rejection, making them ideal for recording from large distances. However, cheaper shotgun mics tend to have poor frequency response leading to a tinny or hollow sound. Also, because of the strong side rejection, shotguns also tend to lack a very strong sense of presence because they fail to pick up many of the ambient cues from the space of the recording environment.

As you can see, the recordist has a lot of options to consider when choosing microphones. In most cases, the best recordings can be achieved by using a combination of microphones. That alone can be an expensive proposition. For the most flexibility, one should consider recording multiple tracks, one for each pair of microphones, in order to allow the tracks to be carefully mixed down later on. Have the cash for an A-DAT?

For an excellent collection of microphone & recording information,
see the DAT-Heads Microphone FAQ:
http://www.harmony-central.com/Other/mic-faq.txt

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Last modified 4/26/97.