MY MIC SOUNDS NICE, CHECK 1
Jan 30, 2007 6:51 PM
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As one of the most subjective pieces of equipment in the studio, microphones forever lead record producers and engineers on chases for that elusive (or nonexistent) status of perfection. Choosing certain microphone types for vocals and instruments can define an artist’s sound, an engineer’s reputation or a producer’s “genius.”
Whether you’re an MC looking for the right microphone to give you an edge or a band starting a mic closet, you’ll find three basic construction types at your disposal: dynamic, condenser and ribbon. To appreciate the differences that come with using one type over another (apart from actually hearing them), you need to understand their unique physical characteristics.
WHAT’S THE DIFF?
If you’ve ever tossed bandmates a venerable Shure SM57, you’re already familiar with several of the qualities that make dynamic mics special. As your drummer will attest to, they can handle huge sonic impacts with ease, and they eat the sustained high sound-pressure levels (SPLs) of a guitar cabinet that’s cranked to “11” for lunch. Dynamic mics are also relatively inexpensive and extremely durable, making them ideal for use in live show settings.
Using a fairly stodgy magnetic-field approach to convert sound impulses into electrical energy, early dynamics were described as sounding somewhat boxy and not very receptive to delicate nuances. Modern dynamic mics have come a long way in better addressing the high and low ends of the frequency spectrum (as well as sensitivity), but the underlying inefficiencies of their heavy, moving voice coil design has kept them from nudging the more costly condenser microphone out of a job.
Condensers, also known as capacitors by our British friends, are highly sensitive and much more accurate than dynamic mics, with better frequency and transient response. Consisting of small- and large-diaphragm varieties, condensers use an extremely thin charged metal—usually gold or metal-coated Mylar—diaphragm suspended in front of an oppositely charged stationary metal plate to capture sound across the entire range of human hearing. This energy-efficient setup requires some pretty lofty tube or solid-state (transistorized) circuitry, traditionally making condenser microphones much more expensive than their dynamic cousins. Also, compared with dynamic microphones, condensers will distort at loud volume levels far easier, and their precious metal capsules are more prone to damage caused by moisture and other physical abuse.
Dating back to the 1930s, ribbon microphones were considered the condenser mics of their era in North America. But in fact, they are an alternative form of dynamic microphones. Composed of a thin corrugated pure-aluminum ribbon suspended in a magnetic field, they combine the smooth, detailed sound of a condenser with the higher SPL tolerance of a dynamic. Long considered a dark horse for the home studio for their exorbitant cost and fragile nature, recent advancements in the ribbon’s design offer some unique and truly exciting benefits to digital recording. They have a distinctly warm and natural tone that’s alive and panoramic with buttery-smooth transient edges, which DAW engineers are finding quite attractive for giving modern recordings a retro vibe. And today’s ribbon mics are durable enough to tackle the loudest rock amplifier for live stage use.
POWER TRIP
Microphones generate extremely low electrical current. Dynamic mics are passive circuits and need no power to operate. Condenser mics, on the other hand, require a power source, provided either in the form of 48V phantom power (as supplied by most pro mixing boards, preamps and audio interfaces) or from an external power supply.
Phantom power travels through one of the wires in your standard XLR cable whereas, in the latter case, power and audio are delivered simultaneously via special, multi-conductor cables and non-standard connectors from a dedicated power supply specific to the microphone. It is at this external box that the mic-level signal first appears as a standard three-pin XLR connector. From there, outboard or console preamplification is used to boost the still-weak signal, once again, to a final ‘working’ level, hopefully with as little noise induction as possible.
Most tube mics (but not all; Audio Technica’s AT-3060 is but one exception) require this external form of power. Transistorized condenser mics require far less power and can even operate from a battery, but more often than not use phantom power. Dynamic microphones usually "ignore" phantom power, so plugging in by accident typically won’t harm them. You almost never want to send phantom power to a ribbon microphone, though – unless that specific model requires it.
PICKUP LINES
Within a given type, microphones can take on radically different sound and response characteristics depending on their “pickup,” or polar patterns. By graphing a microphone’s sensitivity versus the angle of incoming sound, manufacturers give you a visual representation of the electronic fields from which you can capture sound waves—making your job of matching microphones to recording tasks a little easier. Some mics have only one pattern, while others have switchable patterns to choose, including intermediate stages. A few expensive models even let you swap capsules to get different polar patterns. When speaking of polar patterns in general, signals picked up from directly in front of the microphone are called on-axis, while signals arriving from the sides are off-axis.
The most basic polar pattern is omnidirectional. Just as it sounds, this means that the microphone picks up sound from all sides and angles equally. Though technically accurate, this catch-all approach may not be suitable for use in smaller studios where multiple players might be recording close together, or where poor room acoustics aren’t worth picking up.
For this, the cardioid (heart-shaped) pattern is ideal because it has directional response; that is, pickup is best to the front of the mic, and the level decreases as sound arrives from the sides and back. As illustrated by their graphs, the least sensitive spot of a cardioid microphone is directly behind it, where there is practically a void at 180 degrees. While traditionally used in live settings to avoid picking up crowd noise, cardioid mics have a definite place in the studio as well.
A third and very useful polar pattern is the figure-8, so called for its two spherical pickup areas on the front and back of the microphone, while rejecting off-axis signals from the sides. In the early days of pop music, background vocalists or even duets would record from either side of the same microphone to save on studio resources.
Regardless of their factory-prescribed patterns, the responses of all microphones become more omnidirectional at low frequencies and more directional as frequencies rise. Mics also generally add more “color,” or mild distortion, to sounds that come from off-axis, which often makes sources from either side of the mic sound less natural.
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