by Loren Alldrin
Have you ever thought about where recordings really begin? If this question brings to mind a tape deck, mixer or analog-to-digital converter, you're a bit too far down the signal path. While these components are crucial parts of many recording chains, they're not where the process actually beings. Instead, it's the microphone that's the real starting point for most recordings.
The microphone is responsible for the crucial first conversion that turns minute changes in air pressure (sound) into an electrical signal. How well the mic performs this task has a profound effect on the quality of the recording. Capture a brilliant performance with a bad mic (or poor mic placement), and the result is a bad recording. Place the right mic in front of a talented instrumentalist or vocalist, and you'll consistently capture excellent recordings.
Choosing and using microphones well involves a unique mix of artistry and technical savvy, making it one of the more enjoyable - and challenging - aspects of recording. In the next few pages, we'll help you achieve great recordings by covering some key principles of microphone technology, selection and placement.
Microphones: The Inside Story
Microphones use three main methods to convert sound to electricity, a distinction that divides mics into the dynamic, ribbon and condenser classes. The dynamic mic is simplest of the three, and works much like a loudspeaker in reverse. As sound vibrates a thin, round diaphragm, a coil of wire moves back and forth through a magnetic field to generate a changing voltage. This voltage is the microphone signal. In a ribbon mic (which is closely related to the dynamic mic), the ultra-thin wisp of metal that makes up the ribbon sits directly in a magnetic field. When it moves in response to sound, the ribbon generates a corresponding voltage that is the mic's output signal.
Condenser mics suspend an ultra-thin membrane above a stationary, electrically charged backplate. Thanks to the electrical principle of capacitance, any movement of the diaphragm causes a small change in voltage. This tiny signal is then amplified inside the mic body to become the mic signal. Because condenser mics have on- board amplifiers, they require a source of power. The most common way to power condenser mics is with phantom power, a voltage sent down a standard mic cable by a preamplifier or mixer. It's important to note that applying phantom power to a ribbon mic will often destroy the ribbon, and likewise may harm some dynamic mics.
The condenser mic class splits further, based on the size of the diaphragm used to pick up sound. Small- diaphragm condenser mics use diaphragms less than 1/2-inch in diameter. Large-diaphragm condensers frequently boast diaphragms an inch or more in diameter. Diaphragm size affects many aspects of mic performance, including frequency response, directivity, sensitivity and overall sonic character.
Finally, mics differ in their pickup patterns--this describes how a microphone responds to sound coming from all sides (see figure 1). If a mic picks up all sounds equally, it's a non-directional or "omnidirectional" design. More common are mics most sensitive to sounds coming from a heart-shaped area directly in front of them, which describes the "cardioid" pattern. Other patterns include bi-directional (most sensitive to sounds coming from directly in front and behind), supercardioid and hypercardioid. The latter two are more-directional versions of the standard cardioid.
