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Audio Microphone Tech Specs

If you've ever had to buy a mic and try to determine your needs by the specs, you know the challenge. No two manufacturers offer the same set of information, reference points are different and there aren't any real standards for comparison. So how do you navigate the sea of information? After reading through several dozen spec sheets, we've created an essential list of specification categories and their meanings. With this information as a guide, you're armed with the essentials to choose any type of microphone, from lapel to shotgun.

For the most part, you have to worry about only two different types of microphone transducers: dynamic and condenser. Dynamic microphones are durable and virtually impervious to temperature and humidity. The trade-off is larger size, reduced sensitivity and slightly limited frequency response. By contrast, condenser mics offer extended sensitivity and range but fare worse in weather extremes. They also require a power source of some kind, either battery or phantom power. From time to time, you may encounter a ribbon or crystal microphone. These are typically reserved for specialized recording and live-sound applications.

Experts say that human hearing typically reaches from 20Hz to 20,000Hz. Generic microphone frequency responses usually fall within that range, a little shy of the extremes of the scale. While a rated frequency response is nice, you'll learn more about how the mic sounds by viewing a graph or chart of the response. As you're looking, watch for unevenness in the curve and how quickly it drops off at the top and bottom of the scale. In either case, smoother is usually better. A frequency-response chart often includes additional traces indicating the effects of various pads and low cut switches.

Standard video production microphones have a directional or a non-directional pickup pattern. Directional patterns come in several flavors, starting with cardioid. A cardioid pattern picks up sound primarily from the front of the mic, with some pickup on the sides and none at the rear. Super- and hyper-cardioids are simply tighter pickup patterns that help focus the sound and minimize other noises. By contrast, the non-directional pattern picks up sound from every direction, hence the name omni-directional. Some studio microphones also include a figure-8 pattern with equal pickup in front and back and no pickup on the sides - not too useful on a video shoot, but handy in the studio.

Microphone outputs are important, as they determine how you'll attach the mics to your equipment. The standard professional connector is the 3-pin XLR. This offers a balanced output that stays interference-free for hundreds of feet. Of course, not every camcorder has balanced inputs. Several microphones offer consumer-type 1/8" plugs, which match smaller cameras. These connections are typically unbalanced and are prone to interference, so don't try to extend them. You may also see output impedance rated in ohms. Balanced microphones range from 150-600 ohms. Unbalanced mics run up to 10,000 ohms.

Microphone sensitivity ratings are confusing. It seems that every manufacturer uses a different scale or measurement method. On close examination, you'll find terms like Pascal and Dyne, along with abbreviations such as dBV and SPL.

Let's simplify things a bit. The number you're looking for is negative and may be listed as something like -54.5 dBV/Pa. In general, greater numbers mean microphones that are more sensitive. Keep in mind, higher sensitivity doesn't automatically mean a better mic; it just means that it's more sensitive to a given volume level. In some cases - loud instruments, for example - a lower sensitivity means less chance for signal overload.