Ever have outdoor audio problems like these?
- Your dialogue sounds okay except when the Tasmanian Devil seems to be munching on the microphone.
- Your half-time discussion with the football coach yields an impeccable transcription of the marching band behind him but his own words are quite inaudible.
- Your on-camera spokesperson sounds LIKE THIS in close-up, but like this in full shot.
- Your reunion-picnic interview with Great Grandpa Frizzle has no sound at all (and Gramps has since gone home to Pago-Pago).
If you’ve videotaped outdoors, chances are, you’ve fought with wind and background noise and uneven mike levels; and at least once you’ve reviewed your production tape later to find you’ve unwittingly returned to the thrilling days of silent movies.
It doesn’t take a Rembrandt to get good quality visuals, so why is sound so often a pain in the plug? It’s partly because our brains process recorded visual and aural information quite differently. With visuals, we can mentally pick out the important parts and separate them from the background; but with audio tracks we normally don’t do that (though in the real world we routinely filter out extraneous noise). While we ignore small inconsistencies from one image to the next, shot-to-shot sound shifts are both noticeable and irritating.
To accommodate the way we perceive recorded audio, you need to present tracks that are clean, clear, and consistent, even when taped in the ambient racket of the great outdoors. So here are some tips for good outdoor audio.
Location Sound Problems
Field audio mischief is caused by five main villains: wind, background noise, distance, direction, and signal problems.
When wind rushes past certain hard materials it makes them resonate, which is just dandy in an oboe reed but not in a microphone housing. That’s why professional mikes are covered by spheres or tubes of pliant foam. The idea is that sounds aimed directly at the mike can penetrate the porous foam but wind blowing across it is intercepted by material too soft to make noise, as you can see from Figure 1.
If you use an external microphone you should definitely get a foam wind screen for it. They’re cheap and they work well at the job of reducing wind noise. If you use the camera’s built-in mike instead, there’s not much more you can do. The manufacturers have already fitted wind screening of some sort and the mikes are too small (or downright inaccessible) to hang any more protection on. Some models have switches to internally adjust mike sensitivity to filter wind noise.
You can also cut wind noise by shielding the mike from the breeze with a reflector or similar flat sheet, but this technique requires an assistant or a century stand to hold the card in place. And since mikes often have to move with their subjects, fixed wind breaks are not always practical.
Another big outdoor sound problem is background noise: traffic, pedestrians, machinery, you name it. If you’re working close to your actor –say, an on-camera narrator, you can sometimes reduce background noise by masking with off-camera blankets or furniture pads, again held by Century stands.
But most of the time the only fix is to restage the action so that the sound source is not behind the performers where the mike would pick it up. Be very careful about reflections as well. Action staged against a nice blank building opposite the traffic can yield truly terrible sound because the wall dutifully bounces the street noise right back at the microphone.
In looking for suitable backgrounds, keep two points in mind: first, soft screens like trees and other foliage reflect less sound, and open views with no background elements reflect none. Secondly, remember that the angle of incidence equals angle of reflection, as you can see from Figure 2, so move your camcorder out of the sound rebound path.
Distance and Direction
Two other big foes of good sound are the distance from mike to subject and the direction in which that mike is aimed.
When you record audio only (for voiceover narration), get the microphone right in front of the speaker’s mouth. This allows you to get a maximum of voice and an absolute minimum of background noise. When you use a built-in camcorder mike for this purpose, move as close as you can. It doesn’t matter if the picture’s out of focus or poorly lit; you’re not going to use it anyway.
When you do need picture as well as sound, the mike has to be far enough away to stay out of the frame. That’s when mike-to-subject distance can degrade audio quality. If you work with the built in mike, use a wide-angle lens setting and move as close as practical to your subject. (But be careful with wide angle clasps because they exaggerate facial features and can give your vain Aunt Tillie a schnozz like an elderly anteater.)
If possible use an external mike. If the subject is a news-style "standup," your intrepid correspondent can simply hold a visible hand mike in an ideal spot for good audio. If the mike needs to be unobtrusive, clip-on lapel models work well. To get up-close and personal, shotgun mikes (the long skinny kind) on booms work great. However, if you have two or more people on one mike, one person sounds great while the others appear to be phoning in from Siberia.
When miking multiple sources you have four options: a single mike that you can re-aim, a single omnidirectional mike, a pickup recording of off-mike dialogue, or multiple matching mikes.
A movable mike is the easiest solution. Have the interviewer simply point a hand held mike at the interviewee to catch his or her comments.
An omnidirectional mike records everything on all sides of it, so it will pick up both sides of a conversation. The trouble is, it records everything else as well. It works best if the two people are close together.
Homemade mike booms can be as simple as a broomstick, extension cable, and duct tape. The trick is to mount the mike at right angles to the pole, as you can see in Figure 3. That allows the boom operator to switch the mike from one side to the other by quickly rotating the boom. Be careful while handling the boom though, any noise you make with your hands will be transmitted up the boom to the mike. Incidentally, miking downward from above the shot often works better than upward from below. That’s because the down-pointing mike picks up less extraneous noise and the mike can usually be closer to the subject without being seen.
Multiple mikes are ideal, but they require a production mixer to balance them and the skill to use it. The other extreme is a single on-camera mike which is a no-brainer to operate. However, it can never be closer than the camera it’s stuck to. (External mikes mounted on the camera offer only slight improvement. Use them only when you cannot detach and operate them separately.) With an on-camera mike, try recording the two sides of an interview separately. First, tape and mike the subject’s answers. The off-camera sound of the questions will be low-grade but audible. Then turn the camera around and record the interviewer re-asking the same questions. Cutting back and forth in editing will yield an interview with uniformly good sound.
Um, well, sometimes, that is. If the interviewee is standing in front of a nice quiet background and the interviewer opposite is backed by a tractor factory, the two performers will be equally audible, but the overall sound quality will vary so widely that it’s tough to cut back and forth between them.
The obvious fix is to position both parties so that their sound quality is similar. Remaining mismatches can be partially paved over by sound tracks called "ambience" or "presence" which contain nothing but background noise. Typically, the sound recordist will ask for silence and then lay down five minutes or more of ambient sound. In post production, this track will run throughout the scene, blended with the production audio tracks to equalize overall quality.
Quality Sound Equipment
The last great sound problem is entirely a function of hardware: Where sound quality refers to the incoming physical noises, signal quality refers to the electrical transcription of those noises. Poor signal quality usually results from problems with interference or connection.
Microphone cables are notoriously sensitive to electrical interference, especially the unbalanced line systems supplied for amateur use. (If your cable is fitted with mini plugs, it’s unbalanced. If it has big, fat three-prong XLR plugs, it’s balanced.) You can minimize interference by purchasing "shielded" mike cables and keeping them as short as practical.
Interference problems are even more common with wireless mikes, which have to send a signal through the air from the mike to a distant receiver. The models affordable by amateurs and prosumers share frequencies with cheap cordless phones, so they share interference problems. Some mikes let you switch channels, but with others, shift the position of the receiver as close to the mike as possible. Never rely on wireless mikes exclusively for external miking. Always carry cabled mikes as backups.
Connection problems come in two flavors: mismatched electrical levels and poor mechanical contact. Without getting technical, inputs marked line, mike, and phones have different and incompatible electrical characteristics, so don’t try to plug a mike into a line-level input.
Connection problems can be fatal because they may kill the audio signal entirely. The mike-in jack on your camcorder senses when an external mike is plugged into it. This automatically disables the camcorder’s built in mike but the ridiculously incompetent mini plug supplied with amateur mikes can easily lose electrical contact in the socket without losing physical connection. Result: the built-in mike is disabled but the external mike is not enabled, and the system captures zero, zippo, zilch.
Next to an external mike, a good set of headphones is undoubtedly the most vital accessory you can add to your kit. They warn you of every type of location sound problem: wind, background noise, distance, poor transmission, no transmission –the lot. Since headphones are inexpensive, purchase a full-ear design that excludes extraneous noise.
To continue the subject of equipment, let’s discuss the Century stands mentioned earlier. Imagine a three-legged critter with an arm clamped to the top of its telescopic stand (Figure 4a). The arm is held by a clamp made of three disks and a bolt (Figure 4b). A second clamp is screwed on to the end of the adjustable arm.
These clamps are modest masterpieces. Their first two inner faces have accordion surfaces designed to lock together in any position. The other inner faces are grooved to help grip cardboard, foam core, or other flat materials. They’re also channeled to clamp both fat and skinny extension arms at any angle.
You can use them as mike stands, boom holders, or supports for sound insulating materials (not to mention endless applications in lighting.) If you don’t have an assistant to help you with audio, a C-stand (as they’re affectionately known) is the next best thing. You can obtain them inexpensively from mail order suppliers like Markertek or manufacturers like Bogen.
Hey, We’ll fix It in Post
When a location shoot is halted for the tenth time to wrestle with an audio problem, the impatient director is tempted to say, don’t worry about it; they can correct bad sound during editing.
Wishful thinking. Bad sound can never be transformed into good sound in post production. The most you can hope for is to improve it. So discipline yourself to get the best quality audio you can during the shoot.
When the sound quality is not ideal, despite your best efforts, you can improve it somewhat in post production. In purely digital, non-linear editing your control over audio is awesome; but most of us are still doing linear, analog editing. Even there, you can improve sound in three ways: equalize it, homogenize it and fake it.
Equalization can reduce background noise by lowering the volume of the frequencies at which it occurs. The graphic equalizers used in audio systems work well, and so do the digital equalizer applications supplied with many computer sound cards.
The idea is simple: listen to playback as you dial down one range of frequencies after another until you reach the part of the sound spectrum where the unwanted noise occurs. This works well with narrow-range noises like a fluorescent hum, but less well with many outdoor sounds like traffic and wind which range over such a broad spectrum that you can’t dial them down without degrading overall sound quality. I recall one aggressive attempt to reduce city traffic in an outdoor interview. The equalization muted the traffic all right, but the interviewer sounded like Donald Duck.
Remember the five minutes of ambient sound you taped on location? You can use it to homogenize your tracks and to reduce the sound differences between different camera angles and mike positions. Simply run the presence track continuously as you lay down the individual shots, blending the output with a simple mixer (Mackie and others make great ones, and you can get competent models from Radio Shack dirt cheap). For more control, rebalance the mix for each separate shot, boosting the presence track under low-noise shots to make them sound more like the high-noise angles.
When all else fails, fake it by replacing bad audio in one shot with better sound from another shot. For example, if you cover the same action in close-ups and in a long shot master, use the close-up sound over the longshots. Any small lipsync problems will be very difficult to spot in the wider angles.
To replace sound tracks, your recording VCR needs an audio dub feature. Though this control works somewhat differently in VHS and 8mm, the basic idea is the same. Lay down picture and sound via the normal recording process. Then re-cue the record deck and use the audio dub control to roll in replacement sound.
Unless you are working in digital post (with multiple sound tracks under complete control), it’s better to solve audio problems out in the field as you record the production sound. To do so, aim your mikes away from background noise, get them as close as possible to your actors, and keep their direction and distance consistent from setup to setup.
And for goodness sake, wear your headphones at all times. You can’t fix what you can’t hear.