Tools and Techniques for the Sound of Success
Concentrating exclusively on the video portion of your videomaking, ignoring the audio, is like believing that a car’s front wheels are more important than those at the rear.
But in almost every audio/video association, it’s as if the audio is the passed-over junior partner. Even in camcorder design, the video componentry dominates, taking up more space and offering more features. For sure, videomakers of all abilities have been guilty of the sins of audio neglect.
Commonly, neither the average videographer nor his or her subject has the vaguest idea about how to get the most out of the most obvious and vital audio tool: the microphone.
It’s not that it’s difficult to learn how to use a microphone properly. It’s just that the mike isn’t usually regarded as the crucial recording instrument that can make or break your video’s audio.
Microphones are often compared to the human ear-not because the ear is perfectly analogous, but because we have no other choice.
The mike “hears” every sound within it’s range, all recorded by the camera’s audio system. The farther the sound source is from the camcorder’s boom-mounted mike, the greater the noise level, since the mike cannot distinguish between desirable and unwanted sound.
The essential difference is that the human ear, in conjunction with the brain, is sound selective. It can reject some or all noise, something no mike can do. Because noise is so prevalent, it may be difficult to become aware of it while using a camcorder.
The fact is, most of us don’t know how to listen to mike-fed sound. Deliberate listening takes concentration, but the reward is that you’ll hear unwanted sounds, though your ears will try to downplay them.
After the microphone has been positioned (assuming that an accessory camera mike is being used), monitor its input with headphones plugged into the camcorder. Also, try intent listening without headphones.
Conscious, deliberate listening-concentrating on unwanted sounds-may reveal the noise of an overhead electric fan, an air conditioner, outside street noise, miscellaneous house sounds.
The mike will pick up all sounds within its reach, so you may need to turn off sources of noise when recording indoors, or find a quieter outdoor location. Remember, the microphone is nondiscriminating.
It Takes Two
The minimum number of mikes to use for videomaking is two: one as part of the camcorder, the other as an add-on accessory, via your camcorder’s microphone jack.
The chief advantage of a camcorder’s built-in microphone is its convenience.
But even when fully extended, a sliding camcorder-mounted boom will often be far from the sound source. Consequently, its signal-to-noise ratio (comparison of audio signal and accompanying noise) suffers, the result of picking up extraneous noise.
Further, if the microphone is retracted or if it has a fixed position on the camcorder, it can pick up the noise of motors inside the camera.
An outboard microphone is much more flexible with respect to positioning. By using a number of such microphones having different sensitivity patterns (responsiveness to reproducible sound), you can get much better control of the sound.
If you insist on using the camcorder’s built-in mike, the sensitivity level is limited to what the manufacturer has provided. Thus, a plug-in mike is more than just an add-on feature, it’s an essential videomaking tool.
The same goes for earphones or headsets used to monitor your audio. They are not in the video processing line; images and sound can be obtained with or without them. Yet they can make a significant contribution to the overall quality of your videomaking.
Judging by the Response
Size is not a yardstick by which to evaluate the quality of a microphone. Some mikes that have been miniaturized retain or improve performance.
The two most commonly used types of microphones are the omnidirectional (known as an omni) and the heart-shaped cardioid.
The response pattern of the omni is spherical, a three-dimensional shape. The omni-fed camcorder is sensitive to all sounds above, below, in front and back. The cardioid pattern is less sensitive to rear sounds, useful for discriminating noise from behind the camera.
Some other microphone types-the supercardioid, the wireless, the shotgun, the bidirectional, and the lavalier-are variations of the omni and cardioid configurations.
Many mikes have a frequency response of only 30 to 15,000 Hz, about the same as is supplied by the average TV set. You won’t need more than that because you probably can’t hear anything above this range, anyway.
Female videomakers have an advantage here; women are slightly more sensitive to higher-frequency sound than men. It’s a dubious advantage; many would be willing to swap it for equal pay for equal work.
If you like using the tone control on your radio receiver or the equalizer of your hi-fi system, you can buy a mike that offers these electronic goodies.
Some have built-in tone compensation filters that can change their performance characteristics, emphasizing bass, mid-range, or treble.
The feature also gives you better control over the mike’s working distance (separation, usually specified in inches, between the sound source and the microphone’s diaphragm).
You’ll find that adjusting this control is easier than locating the mike’s best position by a fraction of an inch.
Hissing Should Be Missing
In addition to signal-to-noise ratio, sensitivity, responsepatterns, and frequency response, impedance is also an important microphone characteristic.
But just like microphone size, impedance is no indication of quality. A low-impedance mike can be superior to a high-impedance model, or vice versa. The difference is that the low-impedance mike produces less hiss while the high-impedance unit supplies a higher audio signal level.
Impedance matching in hi-fi systems is absolute; with microphones it’s either low or high, with no numbered gradation. If the spec listing (included with the owner’s manual) for your camcorder’s mike input jack specifies low impedance, the mike and its associated cable should both be so.
If high impedance is specified, a high impedance cable and mike should be used. You can also use a matching transformer to avoid being trapped by having to use one or the other.
If possible, keep the cable shorter than 25 feet. This length should be adequate for all in-home recording, as well as for conference and news recording. The longer the cable, the greater the chance of losing high-frequency sound.
Poised for Success
It would be wonderful if the exact distance a mike should be positioned from a sound source was a constant. It’s not.
The correct placement of an accessory microphone is comparable to the way videomakers aim camcorders. Quality images are the result of circumstantial strategy-and experimentation.
Positioning to capture the best sound involves a number of factors: optimum separation of the microphone from the sound source, the angle of the microphone, and the distance of the mike from other sound sources affecting the main source.
For in-home use of a camcorder, it’s generally not possible to change the acoustic environment in which the recording will take place. However, it is possible to control the recording of sound by microphone placement.
The mike’s distance from the floor, ceiling, and walls are especially important variables. Appropriate positioning also depends on the microphone’s sensitivity pattern.
From Far and Near
The two starting points for the placement ofamicrophone are both extremes. Since they represent limits, mike positioning will take place somewhere within this range.
The first limit is to mike up close; the other is to keep the microphone and sound source widely separated.
The advantage of working in closely is that it minimizes or eliminates the impact of room acoustics absorbed in the second approach. But close-in miking is unsatisfactory since it is equivalent to having ears up against the sound source-an unnatural listening position.
Again, the ideal placement-unique to the recording circumstance-lies between the extremes.
Professional speakers and vocalists know how to hold a mike. If they don’t, they aren’t really professionals. Some pros practice a technique called “miking in,” positioning the mike close to the lips to minimize extraneous noise or to produce certain sound effects.
A disadvantage of miking in is that it can pick up breathing, manipulation of the mike by the fingers, and other undesirable noises. Even if you don’t hear them while recording, they can show up in playback.
Some listeners call it realism, others regard it as noise; to each his own.
Handle With Care
The microphone represents the beginning of a chain of events that ultimately lead to sound recorded on the videotape inside the camcorder. See that the process isn’t spoiled from the start.
The mike needs no coddling. It simply works as an intermediary between the sound and your camcorder. But it is neither a toy nor a baton, although some users find it amusing to toss it or wave it while others try to swallow it.
These examples of idiocy won’t damage a well-made mike, but the punishment may fit the crime later. Mechanical shocks are converted to noise and, oddly, the more sensitive and expensive the mike, the greater its response to mishandling.
Also, use the mike cable with care as well. Pick it up; don’t drag it, pull it, or walk on it. It may look like a length of rope but that’s where the similarity ends.
Even an ear-shattering 130 dB-sound so loud that a rifling jackhammer is a lullaby in comparison-won’t damage your mike. What it does to your ears is another matter.
If you’re having a problem with distortion and are blaming your mike, look elsewhere. Some professional mikes can be used in the mouth of trumpets which transmit up to 146 dB; even under such extreme working conditions the output of the mike can remain clean.
Also on the topic of loudness, if you plan to give your mike a boost by inserting an amplifier between it and the camcorder input, you face the possibility of overloading the camcorder’s input circuitry. The result is sound distortion.
Two solutions: Put a greater distance between the sound source and the mike, or else turn down the amplifier’s gain.
The mike amplifier in your camcorder has a limit to the amount of signal it can handle. They aren’t all alike.
Some amplifiers may have a -60 dB input signal rating, meaning they can handle a signal of this level before overloading. Others can tolerate as much as a -22dB mike input without distortion. (Smaller negative numbers closer to 0 dB indicate higher output.)
You could buy a signal attenuation pad for use between the mike cable and the input to the camcorder. Supplying a 10 to 20 dB attenuation, it can be switched out when not needed.
If you’re thinking of getting a low-output mike to solve this problem, abandon the thought. The penalty is that you will lose the advantage of a better signal-to-noise ratio in normal use. It’s always a safe bet to buy the best mike you can afford-for all your audio uses.
Demonstrating a commitment to the videomaker market, companies including Azden, Maxon, Nady, and Sima offer microphone systems specially designed for use with video gear.
Meant to Complement
The microphone and the video camera are the original odd couple. The camera likes the outdoors-the large amount of light available, nature’s generous distribution of color.
The mike prefers working indoors, taking advantage of recording the combination of dry sound (coming directly from the subject) and wet sound (reverberant sound providing richness).
It’s possible to make sound subservient to video, or have video kowtow to sound. But it’s far better to find a mutually supportive balance.
Martin Clifford, a member of the Electronics Hall of Fame, is the author of Microphones and The Camcorder-Use, Care, and Repair (Prentice-Hall), in addition to more than 80 other technical books.