Tuesday, April 24, 2012
Get Mic’d Up!
How to place a microphone to take your sound recording to the next level
|This Article Features Photo Zoom|
It's no secret that when shooting video with your DSLR, you need an external microphone if you want to capture quality audio in the field. So you've purchased an ultradirectional shotgun mic or a wide-angle stereo model with a camera-shoe mount and an 1⁄8-inch audio output that attaches directly to your camera. And with dozens of offerings on the market, ranging from about $50 to several hundred dollars, you've already completed the hard part. Now the fun begins!"
READY FOR THAT CLOSE-UP
A main enemy to good sound is ambient background noise. As any mic is placed farther from the sound source, the level of unwanted noise increases, and this can come in many forms—audience noise, mechanical/air conditioning sounds, background traffic, etc.—as well as the reverberation caused by the room itself. The best way to circumvent this is to get your mic as close to the source as possible. Ultradirectional mics can help in this regard, but only to a degree. As an analogy, consider shooting a football game from the rim of a stadium in dense fog. A telephoto lens will get you close to the action, but as you're shooting through fog, the picture won't be as clear as a shot taken a few feet from the action. The same applies to audio.
With audio, the rule is, the closer the microphone is placed, the better the sound. As with all rules, there are a few exceptions. Let's say you're filming a string-quartet recital. In this case, placing the mic too close to the musicians may not capture a good balance of the instruments. And this is one case where you probably do want to have a bit of the overall room ambience to add a degree of smoothness and depth to the sound, so placing the mic 15 to 20 feet back from the musicians may be ideal. But be aware that what works great for instrumental recording doesn't always apply to the human voice, where that same reverberant quality actually degrades intelligibility, making the words harder to hear. So if you're shooting a play, seminar or lecture where you want to understand what's being said, the "closer=better" rule applies.
POINT, POINT AND SHOOT
If you simply attach the microphone to your DSLR rig, pointing the mic wherever your lens is aimed, you might be missing out on some of the audio action. For example, I frequently travel to technology conventions and shoot clips of people doing product demonstrations. Usually, these begin with a close-up of the representative doing the intro, and I then tilt down to show the product as the presentation continues. With the mic fixed on the camera, the audio is great at the beginning, and then will drop off in level as the camera tilts downward toward the product and away from the speaker's mouth. A quick and inexpensive solution here is to take the mic off the camera, connect it via a short (five- or six-foot) audio extension cable, and have a friend or assistant hold the mic pointed toward the voice while you pan, tilt and zoom in on the details. As an alternative, if you're working alone, remember that most mics can be mounted on a tripod or small desk stand for just such occasions.
Shotgun microphones operate under the principle of acoustical cancellation. Here, sounds entering from the front of the mic are unaffected, while sounds coming through the sides of the mic's long interference tube are effectively cancelled out. Here, again, it's important to consider what you're shooting and the sound source. As another example, let's say you're using a shotgun mic to shoot a speech, lecture or arena rock show—essentially any event where the audio reaching the audience comes from a public address feed. In this case, your audio will sound much better if the mic is pointed directly at one of the main speakers off to the side rather than fixed directly on the podium or lead singer—the direction where your camera is pointed. This situation comes up often enough that a couple of years ago I bought a few adjustable swiveling mic mounts for my shotgun mics. It definitely was a worthwhile investment.
Another factor to keep in mind when using shotgun mics is that they do an effective job of picking up the sounds that happen in front of them, but they also will capture any sounds behind your sound source. So if you're trying to record someone speaking, and there's a freeway or a busy street behind that person, your shotgun will emphasize that background noise along with the dialogue. The solution in this case is simply to raise or lower your mic so it points upward or downward—still in the direction of the subject, but angled enough so that it's not in line with any offending noise sources. That may require the help of an assistant to hold the mic, either handheld or on a boom, but the improvement this makes in overall sound quality is substantial.
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