Sound Track: Miking Basics

by Loren Alldrin
September 1996

There's more to choosing and using microphones than meets the ear. Here are some basic principles of miking for video.

When it comes to recording sound, the microphone has a greater effect on sound quality than any electronic gizmo in the signal chain. If you've got a crisp, clear recording from your mike, it takes a pretty good effort to mess it up later. Likewise, if the mike signal reaching your camcorder is poor, there's not much you can do about it after the fact.

Thankfully, there's nothing all that tricky about choosing and applying microphones for videomaking. We've covered the topic of microphones again and again in these pages, so you should have a pretty good grasp on how mikes work. This month, we'll explore some of the basics of actually using the mike(s) you already own.

Image Isn't Everything--Distance is
Even if you forget everything else, there's one rule of miking you should permanently burn into your mind: with microphones, distance is everything. To elaborate, the distance between the mike and the sound source is the number-one factor affecting that mike's performance. In most cases, a $50 mike 12 inches from the source will sound much better than a $500 mike at 20 feet.

This is due to the nature of sound. Unlike light rays, which we can filter very selectively through the lens, there's no tidy way to "zoom in" on specific sound waves. There's no microphone equivalent to the center-field camera at a baseball game, the camera that captures the subtlest movement of the catcher's hand from 300 feet away. Even high-tech surveillance microphones can't block out unwanted sounds to that degree.

So what can you do to get some aural distinction between your subject and the competing noise? The answer is simple: get the mike as close as practical to your sound source. If you're deciding between a lavalier attached right to your speaking talent and a directional mike placed several feet away, go with the lavalier. If you're trying to get clean, full sound from your voice-over talent, do what the pros do: place a high-quality directional mike 6 to 12 inches from his or her mouth.

The "distance is everything" rule explains why the camcorder's built-in mike rarely delivers good sound--it's just too far from the subject. If you have to use the on-camera mike, try to do your shooting close to the subject (by using wider zoom settings). Have your subject(s) speak loudly, and move to the quietest location available. And because the on-camera mike is closer to you (the operator) than the subject, stay as quiet as possible.

Picking a Mike
Getting good sound on tape requires selecting the right mike for the job, and placing it correctly. With all the different physical styles, directional patterns, and element types out there, choosing the best mike can be tricky.

As mentioned earlier, directional mikes aren't as directional as you might think. The most common directional pattern is called "cardioid," due to its heart-like shape. When you look at the polar pattern chart for a cardioid mike, notice that the mike's sensitivity is almost as great at its sides as directly in front. This means that a cardioid mike will do a good job picking up sounds above, below and to the sides--it's only directly to the rear that the cardioid pattern has a high degree of sound rejection.

If you're trying to record a large sound source (a group of several people, for example), a cardioid mike's wide pickup pattern will be a plus. If you're trying to "focus in" on a relatively small or distant sound source, the cardioid mike may not be directional enough. Mikes with tighter patterns are available (such as hypercardioid, supercardioid, shotgun, etc.), but they have some drawbacks as well. First, tighter pickup patterns often result in a less "natural" sound. Second, the tighter patterns actually have areas of increased sensitivity radiating around the back of the mike. If the sound is coming in at a certain angle, a highly directional mike might pick up more sound from behind than a standard cardioid.

And while a directional mike will have the aural effect of "closing the gap" somewhat between mike and source, it's not the ultimate solution; closer is still better. An omnidirectional mike (which picks up sound evenly from all directions) placed close to the source will often sound better than a more distant directional mike. Some of the most natural-sounding mikes are omnidirectional lavaliers, because they capitalize on the mike's close proximity to the sound source.

Don't be taken in by so-called "zoom" or variable-pattern mikes. These mikes go from wide stereo pickup to a tighter (mono) pattern, and some of them actually track the motion of the zoom lens. But remember that no mike can match the "pickup pattern" of your camcorder's zoom lens, and these mikes often create strange-sounding artifacts if you zoom while taping. If you can control the zoom mike's pattern manually, your best bet is to find the pattern setting that gives the most natural and uncolored sounds, and leave it there. If you can't disable your zoom mike, you've got further incentive to not zoom mid-shot (which is a good habit, anyway).

Something else to watch for when selecting mikes is their impedance rating. High-impedance mikes are usually quite inexpensive, but have a serious drawback--the longer the cable run, the more dull they sound. Low-impedance mikes usually cost more, but can drive a good-sounding signal through hundreds of feet of cable. Though not directly related, the type of connector is often a giveaway to the mike's impedance. A three-prong (balanced) connector on the mike itself usually means the mike is low impedance. A permanently attached 1/4-inch cable often indicates that the mike is high impedance. This type of mike is generally suitable only for very short cable runs (20 feet or less).

Every type and model of mike has its own particular sound. The science of converting sound waves into electricity is not cut-and-dried--the design of the mike has a huge bearing on the resulting sound. Even in the same price range and class, you may notice that one lavalier mike sounds "boxy" and "dark," while another sounds "open" and "clear." Lay some sounds on tape from each mike before you shoot, and listen to the results. Switching one mike for another can mean the difference between ho-hum sound and a track that practically jumps out of the speakers.

The mike's intended application also has a major bearing on the resulting sound. Some directional mikes are meant to be placed quite close to their sound source. This position creates a buildup of bass frequencies due to what's called the "proximity effect." Most handheld vocal mikes compensate for this by generating a similar boost in the high-frequency "presence" range.

If you use a vocal mike to record a sound source a few feet or more away, you won't have any proximity effect or bass buildup. You will, however, still have boosted high frequencies. The result? Thin, tinny sound. Instrument mikes, on the other hand, don't usually sit so close to their sound source. Hence these mikes don't have a high-frequency boost to compensate for the proximity effect. Place an instrument mike a few inches from your talent's mouth, and you'll get dark, bassy sound. Proximity effect is working against you, with no compensating high-frequency boost from the mike.

Placing your Mikes
The second half of the miking art involves where you place your mikes, and how you apply the "closer is better" rule. As we mentioned at the top of the column, mike placement is the biggest factor influencing a mike's sound quality. Mike placement controls the balance between ambient sound (or noise) and your subject.

Sometimes, if you're trying to accentuate the surrounding clutter of sound, you'll actually want to place your mike a good distance from your sound source. Let's say two actors are struggling to hear each other over the roar of a stadium crowd. Putting mikes on or near the talent would block out a great deal of the ambient sound, making their voices undesirably clear. Placing a mike five or 10 feet away would allow the surrounding noise to compete nicely with their voices. Trying to lift the voice of a training video host over the nearby machinery demands the opposite approach: get the mike as close as possible.

The majority of on-screen dialogue heard in television and movies is picked up with a directional boom microphone suspended just out of the frame. This offers two advantages to the director: freedom of movement for the actors, and a relatively short mike-to-subject distance. You can set up your own simple boom with any number of different items: a broomstick, a mike stand without its base attached, a sturdy fishing pole, whatever. Simply find a way to attach a mike to the end, run a cable down the length of the boom, and train someone to keep it close to the action and out of the frame. You may want to mount the mike with foam or elastic bands, to isolate it from mechanical vibrations (see next section).

Try to avoid picking up the same sound with multiple mikes, especially when they're located almost, but not exactly the same distance from the source. This can cause cancellation. You're better off moving one mike closer to the source, or eliminating the second altogether. Slightly different rules apply for stereo miking, which is the topic of its own column. For recording numerous different sound sources in mono, you have two options: place one mike an equal distance from all sources.

When setting up your mike (or mikes), don't be afraid to experiment with "unusual" placement. A lavalier mike, for example, is not just for lavaliers. Why not conceal a lav mike in a plant between two actors, or hang it overhead just out of the frame? A handheld vocal mike, because of its presence boost, may sound great picking up the muffled giggles of two kids playing in makeshift sleeping-bag fort.

When you're struggling with difficult mike placement, understand that it's better to be slightly off-axis from a directional mike than too far away. In other words, if you can get a directional mike close to the sound source but not pointing directly at it, this is usually preferable to placing the mike a great distance away. Directional mikes aren't all that selective, and many deliver very good off-axis sound.

Other Considerations
Microphones turn vibrations in the air into an electrical signal. Unfortunately, the element inside a microphone converts physical movement into sound as well. This is why some camcorder's built-in mikes record as much transport, zoom, and finger noise as they do desired sound.

Good handheld mikes suspend the element in foam to minimize handling noise. Cheaper handheld models (or those instrument mikes not designed for handheld use) may have little or no suspension, a design shortcut that can turn even the tiniest hand movement into the aural equivalent of an elephant stampede. Again, it pays to consider the original application of the mike before plugging it in. Most lavalier mikes, because of their small size, have no suspension system. This makes the lav a poor choice for any application where someone will be touching the mike directly.

It's important to note that you can (and should) break all these "rules" under certain circumstances. The final authority for any miking decision should always be your own two ears. Record some test footage, and listen back with headphones. Experiment with different mike placement. Try different mikes. If you're having no luck with a stand-mounted directional mike, try substituting a boundary (pressure-zone) mike. Is your handheld mike not cutting it? Try a lavalier instead.

Remember--when it comes to microphones, if it sounds right, it is right.

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