Crossing your fingers and hoping for the best from a camcorder’s build-in mike sometimes works. But exploring the proper use of an external micropone can lead to consistent audio success!
Camcorder enthusiasts pay plenty of attention to the optical and imaging systems that produce the video picture, rattling off zoom ratios, lux sensitivity, and CCD pixel counts as fluidly as jocks might recite sports scores.
But when it comes to the audio pickup system-the microphone that starts the gears turning in the camcorder’s sound system-there’s a tendency to ignore details, literally throwing caution to the wind (and wind noise!).
Granted, sound is not the most glamorous part of videomaking, but it’s often the most important. Try watching television for 10 minutes with the sound turned all the way down, and see how much you understand just from the picture. Ultimately, sound quality can make or break your production.
For many applications-especially casual videotaping of family events, travel, and the like-a camcorder’s built-in mike is sufficient.
But knowing when to plug in an external microphone, and what type to use, can mean the difference between unintelligible, garbled sound and crisp, clear audio.
The human ear can hear an extremely wide range of sound levels; more importantly it can discriminate between the sound we want to hear and background noise.
At a crowded, noisy party, we can focus on a single person speaking and make sense of what he or she is saying by watching lips and mentally “block-out” unwanted sounds. If you made a recording from the same locaton, however you’d likely find what the person said to be totally unintelligible.
The use of external microphones is largely an effort to compensate for this discriminatory difference between the microphone and human hearing. In essence, you’ll be using microphone
location, sensitivity, and pickup patterns to isolate sounds, rather than the intelligence of the human ear/brain system.
Almost every camcorder has a mirophone jack that permits you to disconnect and replace the built-in microphone with an external one. It costs only a few extra cents to offer this feature, and camcorder manufacturers recognize that there are many recording situations for which the built-in microphone is simply inadequate.
When should you bypass the camcorder’s microphone and plug in an external one? Most often, whenever the sound source is too far away or too weak to be picked up properly by the camcorder’s microphone.
In a classroom situation, for example, where the camcorder may be located 20 feet from the lecturer, you can usually use the zoom lens to get a decently framed medium shot (waist up) of the speaker.
But audio recorded from a back-row location is likely to be muddy-filled with reverberations from the walls of the room, noise of ruffling papers, chairs moving, extraneous speaking, etc.
When you’re seated in this position you’re mentally able to tune out all these other sounds and concentrate on the lecture, but the camcorder’s microphone has no such intelligence. Wedding services and bar mitzvahs present similar recording problems.
The solution is to place a microphone closer to the source. A tie-clip microphone is usually best; a desktop microphone placed on the lectern is a good second choice. Third choice would be a highly directional “shotgun” microphone that functions much like an “audio zoom lens.”
Now Hear This!
External microphones are also necessary for recording relatively weak sounds, even when they’re near the camcorder. A soft-spoken person standing seven feet from a camcorder may be audible to you, but relatively inaudible to the camcorder’s built-in microphone.
This is especially true when microphones are located behind the lens, where they tend to pick the whirring sounds of the camcorder’s zoom and autofocus motors.
Similarly, if you’re handling the camcorder a lot- operating a title generator, fade control, panning, and so on-the built-in microphone will pick up these sound to the detriment of what you’re trying to record.
Whatever happens nearest the microphone will record loudest; even relatively “quiet” sounds of buttons being pressed a few inches from the microphone may be recorded louder than someone speaking a few feet away.
In dramatic productions, an external microphone is often necessary to pick up sound that’s not occurring directly in front of the camera.
For example, in a scene of two people talking, you may want a reaction shot of a third person listening. The camcorder will be pointing away from the speaker, toward the listener, and the sound will be recorded much weaker than if the mike were pointed at the person speaking.
You’ll also need to go to an external microphone in outdoor situations when wind noise makes a decent recording almost impossible. Wind noise doesn’t record like the howling wind you hear in
horror movies. (If it did, there would be problem!)
will sound like a constant popping or banging, because shifting air pressure overloads the microphone’s diaphragm, thrashing it from one extreme to another. Because the noise is created
within the microphone itself you must spot it by wearing headphones as you record.
To reduce wind noise, put a foam screen over your external mike to absorb some of the wind’s
energy, and shield the microphone with clothing or a piece of cardboard.
Finally, you’ll sometimes need to use an external microphone when the sound is too loud for the camcorder’s built-in microphone, creating distortion. This may occur at a rock concert if you’re shooting from right next to the speakers.
By plugging in a less sensitive microphone, or one less prone to overload, you often can prevent this distortion.
Most microphone falls into two general types-condenser and dynamic. (A third, more obscure “ribbon” microphone is found occasionally in professional recording studios, but is rarely used for videomaking.) Most build-in camcorder microphone are of the conderser variety.
Technically, condenser microphones work on the electronic principle of pacitance. (“Condenser” is an old electrical term for “capacitor”-a basic electronic component.) A capacitor, or con-
denser, normally consists of two thin electrical plates which store oppositely charged electrical particles. It functions a bit like a battery, except that it holds much less electrical power.
The electrical charge between the plates changes with the distance between the plates, and a condenser microphone takes advantage of this principle by allowing one of the plates to vibrate with the air. Since sound consists of subtle, rapid changes in air pressure, or vibrations in the air, the condenser microphone responds by producing corresponding changes in electrical energy.
Condenser microphones are generally crisper sounding and more sensitive to faint signals than dynamic models, but they have drawbacks: They’re easily overloaded by loud signals (causing distortion); they’re more susceptible to wind noise; and they require power for their built-in circuitry.
The best condenser microphones (used in recording studios) get power from the mixing console, and are called “phantom power” microphones. More common in video applications are condenser microphones that require a small battery which must be periodically replaced. The least expensive condenser microphones, called “electret condenser” types, have a permanent electrical charge (like a tiny battery) that lasts for at least a decade.
Condenser microphones can be built in smaller sizes than dynamic microphones. Practically all lavalier and tie- clip microphones are of the condenser variety, the standard for TV talk shows and news broadcasts. It’s best to use these microphones when people are sitting, since they pick up unwanted sound from clothing when people move around.
Dynamic microphones tend to be more ruggedly built than condenser types. They can usually handle very loud sounds without distorting, and require no batteries. They deliver a warmer sound quality than condensers, and they’re less vulnerable to wind noise.
Technically, dynamic microphones take advantage of the relationship between electricity and magnetism in much the same way a speaker does, except in reverse.
Most people know that running electricity through a coil of wire creates magnetism. The converse is also true- moving a magnet through a coil of wire creates electricity in the wire. This process, called induction (because electricity is magnetically induced), is the principle behind practically all electrical power generators, including the alternator in your car.
The dynamic microphone works like an extremely low-power electrical generator: A diaphragm that responds to subtle vibrations in the air is attached to a thin coil of wire, wrapped around a magnet. Sound makes the diaphragm vibrate, creating a very small electrical current in the microphone’s coil.
Almost all build-in microphones found on camcorders and portable cassette recorders are of the condenser variety-not because they’re necessarily better, but because they make better cheap microphones than dynamics. If you only have a dollar or two to spend on the microphone, condenser technology is clearly superior.
On the other hand, if you’re willing to spend $50 or $100 on a good microphone, you may find better value in the dynamic types.
Pick a Pickup Pattern
A microphone’s pickup pattern can be omnidirectional (picking up sound from all around
the microphone); directional (also called unidirectional or “cardioid”-because of its heart shape); superdirectional (“super cardioid”); hyperdirectional (also called “shotgun” and “hypercardioid”); or bidirectional (“figure eight”).
Directional microphones allow you to focus on the sound source while rejecting extraneous noises coming from other directions. You’ll find, however, that the more direction a microphone is, the more idfficult it is to use.
Hyerdirectional shotgun microphones require very careful aiming towork properly. Some models even include cross-hair sights. An angle error of just a degree or two can mean the difference between great and garbled sound.
The advantage of these microphones, which makes them worth the trouble, is that they allow you to pick up sound much farther (several dozen feet) from the sound source than any other mike.
Each microphone technology (dynamic and condenser) is available with each of the pickup patterns. Some microphones even offer selectable patterns.
Bidirectional microphones can occasionally be useful for picldig up sources that are 180 degrees apart-two singers, for example, or an interviewer and interviewee. Usually, however, you
don’t want the bidirectionality, so it’s useful to be able to flick a switch and make the mike unidirectional.
You’ll hear the term impedance quite a bit as you begin your exploration of microphone technicalities.
Alnost all camcorders and VCRs have high impedance inputs (hi-Z) Theres usually no problem feeding a low-impedance microphone to a high-impedance input (Problems do occur in the other direction, going from a hi-Z microphone to a lo-Z input-but in videomaking the situation
Z is electronics jargon for impedance, measured in units called ohms. Anything under 1000 (or 1K) ohms is considered low impedance, while hi-Z microphones are usually in the range of 10,000 to 50,000 ohms. Hi-Z microphones are usually less expensive to make, so they tend to be found on cheaper consumer equipment, whereas lo-Z microphones are use almost universally in profession recording studios.
The advantage of lo-Z microphones is that they generally produce more electrical power. When running long microphone cables (more than about 10 feet), lo-Z microphones are essential for
less hum (low-pitched buzzing) picked up in the cable.
Low-impedance microphones almost have a three-prong XLR connector (also known as a Canon connector. The three-wire “balanced” system, when used in conjuction with low impedance microphones, further minimizes the hum picked up in the cable.
To plug such a microphone into a camcorder, you should use a “matching transformer” to convert from the three-wire system to the standard two-wire (“unbalanced”) input jacked found on camcorders and VCRs. The lo-Z to hi-Z transformer should be located next to the camcorder, to take advantage of the three-wire microphone cable.
Plan for Placement
Successful sound recording requires experimentation, patience, and practice. A fancy microphone in the wrong hands won’t sound nearly as good as a cheap microphone in the hands of a professional boom operator-someone who’s spent years learning to position the microphone as close to the source as possible without entermg the frame.
The closer the microphone is to the sound source, the higher the ratio between the desired signal and the unwanted noise (Street sounds, air conditioners, refrigerators, office clatter) which inevitably accompanies it.
When recording a person speaking, it’s usually best to point the microphone toward the lower-neck/upper-chest region rather than toward the mouth.
This allows the natural resonance of the upper chest cavity to deliver a fuller, mellower sound quality, and avoids “pops” from percussive consonants like Ps and Bs, as well as sibilance from Ss and Zs. When using a hand-held microphone, speak across it rather than into it to avoid the same problems.
Always carry a roll of gaffer’s tape with you, and neatly tape down long microphone cables. Be especially careful at spots where people may trip over the cords.
Avoid running microphone cables alongside electrical wires, because more hum is induced as these wires get closer. If the microphone cables must cross an AC power cable, it’s best that they do so at a 90-degree angle, to minimize hum.
The only exception to the “get the microphone as close to the source as possible” rule applies with very loud sounds that cause distortion when you get too close. This problem occurs most
frequently with condenser microphones, because it’s harder to overload dynamic types.
For this reason, many fancy condenser microphones include built-in pads that can be switched in
to reduce the levelby 10 or 20 decibels. When such attenuators are available, it’s always preferable get the microphone up close and attenuate it, rather than to keep it farther back without attenuation. The only way you can detect distortion is by listening to the signal as you record it.
Some fancier microphones also have low-frequency cutoff switches that let you attenuate just the bass pitches. Such switches are especially useful to minimize wind rumble, or when microphones are placed in front of amplified speakers.
But unless you specifically need to eliminate the low-pitch range (because of hum or wind problems), you should avoid engaging these low- cut switches.
Another technical annoyance, feedback, results when amplified sound from a speaker reaches a microphone having a response pattern that allows the sound to be picked up and channeled through the amplification process again.
Feedback can be minimized or eliminated several ways: use a cardioid instead of an omnidirectional microphone; adjust the mike’s position so it doesn’t favor loudspeaker sound pickup; move the loudspeaker farther : from the mike or the mike farther from the speaker, or both; lower the sound level of the amplifying system. Sometimes, turning the speakers slightly can be helpful.
You’d never shoot pictures with your video camera without looking at the viewfinder. Similarly, to properly monitor the sound you’re recording with your spiffy new microphone, you must wear headphones. Every camcorder equipped with an external microphone jack also has a headphone jack.
The best headphones for videomaking are the old-fashioned “earmuff” type that block out extraneous sounds. The lighter, portable earphones allow ambient sound to mix with the headphone signal, creating confusion. The cheap single-piece earphone supplied with most camcorders should be avoided for the same reason.
When you plug in higher-quality headphones, though, you may find that the sound level is quite weak. A headphone amplifier, available at many music stores for guitarpractice, can help. Some wireless microphone receivers incorporate built-in headphone amplifiers.
In the audio department you don’t need tons of money to create top-quality recordings. A good microphone and a few accessories like a microphone stand, wind screen, and headphones are all you need-conbined, of course, with your skill in ingenuity.
Cliff Roth teaches audio production at New York’s Institute of Audio Research, and has taught video production in New York and Los Angeles.