Before we get started, there are a couple issues to be aware of. First of all, the onboard mics on DSLRs not only are of low quality, but also are usually placed on the front surface of the camera body, right where they can be blocked by your hand’s natural position gripping the camera. The result is a muffled sound.
Another plus offered by external microphones is variety. Although capable of stereo recording via the external mic input, the internal mics on most DSLRs are single-channel, mono elements. That’s okay for simple talking-head interview shots, but not so good for recording something more complex like music or ambient sounds. But don’t count mono out completely—most highly directional shotgun mics on the market, both professional and prosumer models, intended for distance recording and dialogue capture are mono because stereo isn’t important for the sounds these mics typically record.
What is important, however, is making sure your camera actually has a provision for an external mic. Usually, that’s a 1⁄8-inch input jack next to the USB and HDMI ports on the body. Many, but not all, cameras have a 1⁄8-inch mic input, but check your owner’s manual to be sure. If your camera has no mic input, you can use a mini-pocket-sized digital recorder like the Roland R-26, Tascam DR-07mkII, Sony PCM-M10, Yamaha C24 or Zoom H2n and sync your camera sound with the recorder’s track later during the editing phase.
There are two common categories of microphones used in professional audio. Rugged and simple in design, dynamic mics depend on sound waves striking a diaphragm attached to a coil of wire, which moves within a magnetic field, thus creating an output signal. It’s the exact opposite of the way in which a speaker operates, where a voltage input moves a diaphragm that creates sound waves. A variation of the dynamic approach is the ribbon microphone, which places a thin metallic strip between two large magnets. As the fragile mic ribbon element is highly susceptible to damage from extreme wind gusts, these models are rarely used outside the studio.
Condenser mics employ an electrically charged metallic diaphragm that’s separated from a conductive backplate by a thin air layer. Sound waves vibrating the diaphragm create a very small voltage change that’s amplified by a miniature circuit within the mic body. Both the condenser mic capsule and electronics need a power source, fed either from an internal battery or powered directly by the camera preamp or mixer.
Microphones also are characterized by the directionality of their pickup pattern. Named for the approximate heart shape of its pattern, a cardioid microphone is most sensitive from the front, while rejecting sounds coming from the sides and rear of the mic. Variations with the cardioid family include hypercardioid and supercardioid styles, which are more frontally directional than the cardioid pattern. Most ribbon mics are bidirectional and have a figure-eight pattern, and pick up sounds equally from both sides of the mic body.
Omnidirectional models pick up sounds equally from all directions and are frequently used for on-camera broadcast interviews, where two persons are being covered by a single handheld mic. Speaking of interviews, another handy mic in your kit may be a lavalier type, which essentially puts a miniature mic capsule onto a small clip-on mount. This is ideal for capturing dialogue in a noisy setting or for interfacing with a pocket-sized, wireless body-pack transmitter.
The most directional mics are shotgun models. They’re ideal for general video work, whether camera-mounted or used with a boom pole. This design places a small condenser transducer within a long tube, resulting in an extremely directional pickup pattern. Typically, the length of the tube determines the shotgun’s reach, and available models range from about six inches to two feet in length.
FINDING THE RIGHT MIC
Many microphones designed for the DSLR and camcorder market include an accessory shoe-mount for placing the unit onto your rig. Actually, placement atop your camera isn’t ideal. A boom mic or close-in handheld unit is preferred because bringing your mic closer to the sound source offers better reproduction, with less environmental sounds and noises and more dialogue. That said, sometimes the environment is exactly what you’re trying to capture, say, if you’re shooting a Mardi Gras parade or rain-forest ambience, where a wide sound field is just the ticket. The other side is a dose of reality—if you’re working alone, a camera-mounted mic is a necessary compromise and a huge improvement over the camera’s built-in mic.
The key thing to look for in an on-camera mic is a mount that incorporates some kind of audio shock isolation from handling noise and mechanical clatter, such as autofocus servos. For outdoor use, another must-have is some kind of foam wind filter to protect the mic from being overloaded by blasts of air. For more extreme conditions, a fur-style muff, such as the RODE Deadcat or Que Audio’s Wombat, fits over your mic to provide additional wind protection.
Some models that incorporate shoe-mounts are the Nikon ME-1, RØDE VideoMic/VideoMic Pro and Sennheiser MKE 400. Among those models that include a detachable shoe-mount are the Audio-Technica Pro 24-CM, Azden SGM-1X, Sony ECM-CG1 and Que Audio Mini Shotgun. Any of the latter can easily double as a close-in mic by adding a simple 1⁄8-inch stereo extension cable, found at any Radio Shack®, but keep your overall cable length to a maximum of about 15 feet to avoid picking up interference. Condenser microphones offer the most bang for the buck in terms of audio quality, but need a battery or powering source. Some condenser models—such as the Nikon ME-1, Sony ECM-CG1 and Audio-Technica Pro 24-CM—can operate on plug-in power, which conveniently supplies a voltage directly to your mic through your camera’s 1⁄8-inch audio jack. However, not all DSLRs provide plug-in powering, so check your owner’s manual.
A small investment in an external microphone can make an enormous difference in the overall quality of your DSLR video without breaking the bank. So whether you’re considering an on-camera model, handheld mic or lavalier, take some time and explore the possibilities. You’ll be amazed by how much good audio actually improves the
look of your video.
|Mics with 1/8-inch connections are convenient, but are less rugged than their pro cousins and are limited to cable length. Pro mics’ signals can easily run 100 feet or more without problems. The key feature on pro mics are the three-pin XLR connectors—sometimes referred to as Cannon plugs—and adding the ability to use pro mics with your DSLR adds a huge level of versatility to your rig.
But why would a single-channel, professional microphone need three conductors? The magic comes from balanced-line technology. Using this approach, the mic’s signal goes to pin #2, pin #1 carries the ground (shielding), and pin #3 has an inverted copy of the mic signal. Once the signal reaches its destination—camera, mixer, recorder, etc.—the inverted copy of the signal is flipped and added to the original. Any noise like hum or buzzing that the cable may have picked up along the way from sources such as AC cables, lighting or generators is also inverted and is cancelled out at this stage, while the original signal is unaffected.
That’s great, but how do I get this signal into my camera’s 1/8-inch mic input? Two inexpensive XLR-to-miniplug adapters—the Hosa MIT-156 and the Pearstone LMT100, each about $20—offer easy interfacing of a pro condenser (with onboard battery powering) or dynamic mic to your system and will route this mono signal to both channels of your camera input. To use two such microphones, you could try a passive (nonpowered) XLR mic interface such as the BeachTek DXA-5Da, Sign Video XLR-PRO, Studio 1 Productions XLR2-DV or Whirlwind Audio LMC2.
To use condenser mics requiring pro 48-volt "phantom" powering with your DSLR, you’ll need an outboard mixer/preamp, such as the BeachTek DXA-SLR, JuicedLink CX211 or the just announced Fostex DC-R302—all of which are designed to mount directly under your DSLR to create a compact production package.