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Takeaways

• Recording and playback opperate on the same fundamental principle, but in reverse. Headphones can serve as microphones and vice versa. They do poorly at this, however.
• Line level inputs differ from microphone inputs in an important respect: mic preamps amplify the sound because mics send a low level signal. Plugging a media player, keyboard, or other line level input into a mic jack will likely cause clipping. Similarly, plugging a powered speaker into a headphone amplifier will most likely lead to distortion.
• Dynamic microphones consist of a moving coil creating an electromagnetic field. They require little power and are not very sensative.
• condenser microphones hold an electrical charge in a capasitor. As such they are a great deal more sensative and require 48 volts of power to run. This is accomplished either through a battery in the microphone, or--more commonly--"phantom power" provided over the mic jack by the preamp.
• Electret condensers are significantly smaller than regular condensers and require under 12 volts of power, otherwise known as plug-in power. Providing phantom power to one of these will most likely result in an unimpressive puff of smoke and then no more microphone.
• Unidirectional, or "cardioid" microphones, only accept sound from the front, rejecting all sounds that are "off-axis." "Shotgun," or supercardioid microphones do this to an extreme.
• Bidirectional microphones use a figure-eight or wedge pattern to accept sound from two directions, often the sides and top. This is commonly used in interviews.
• Omnidirectional microphones pick up sounds from all directions.
• Some microphones have a switchable pickup pattern, allowing you to use the same microphone as an omni or cardioid.

Stereo Patterns

• There are several types of stereo recording techniques.
• Microphone placement is important when recording, here are a few common stereo recording techniques and how to best place the mics for optimal placement.

1. The first stereo recording method is A/B stereo recording. Mics generally used are small diaphragm omnidirectional condensers. The mics are spaced about 2 feet apart and sit about a foot or so away from what you are trying to record.
2. X/Y is another stereo recording method in which the microphones used, generally 2 directional small diaphragm condensers are placed at an angle between 90 to 135 degrees so that the capsuls coincide at a single point.
3. ORTF is a stereo recording method in which 2 directional small diaphragm condensers are spread outward at an angle of 110 degrees, spaced about 6 inches apart.
4. The Blumlein pair is a technique in which 2 figure 8 mics are used to record the stereo image. they are placed exactly as an X/Y stereo pair of microphones would be placed. The stereo image recorded is similar to the X/Y image but due to the large diaphragm condensers, generally provides more of a greater ambient sound.
5. Mid/Side stereo recording is a technique in which a large diaphragm figure 8 condenser and a small diaphragm cardioid or omnidirectional microphone are used to capture the stereo image. The figure 8 mic is generally placed sideways about 90 degrees from the source of what it is you want to record, while the other mic is placed either on top of or below the figure 8 mic, pointed directly at the source.

Further Reading:

This page has several tutorials on mic physics and useage. Be sure to check out the "condenser," "dynamic" and "pickup patterns" ones under the "how do microphones work?" section.

Stereo recording techniques

Another excellent resource if shopping for microphones or considering which type you need is http://transom.org/?p=7524