FIELD MIKES: GREAT AUDIO ON LOCATION

Welfare is said to make us lazy and unproductive. Tell that to my kitty cats, Blackie and Whitie, who live in the ultimate welfare state with free food, lodging, medical care, etc. They insist on toiling 9-5 (5 am, that is), hunting down every outdoor creature that moves. Unless it is bigger than they are. Or unless it is the dead of winter; then they take on more human attributes. Anyway, each kitty dutifully deposits a field mouse on the back porch every morning. If we could somehow eat these trophies de jour, we would probably be taking in just the right daily dosage of meat according to the American Heart Association. Hard hunting little guys, Blackie and Whitie. And what does all this have to do with audio on location? Nothing; I just thought "field mikes" was a cute title and needed some way to work it into the story.

Basics

Let's besiege some basics before foraging the fine points:

1. Keep your mike as close to your performer as possible.
   Distance allows echo and background noise to mix with your desired sound. Further, natural bass frequencies drop off quickly with distance. Exception: recording a choir in a church. Here you want the microphone to be near the group but not near a particular member of the group who will dominate the sound. Further, echoes in the room fortify the sound making it robust at
   some distance.
   
   
2. Choose the right mike for the task. Take into consideration whether the microphone needs to reject unwanted echoes and background noise (ie. a directional microphone) or whether the sound is coming from several directions at once, requiring an omnidirectional microphone. For a person speaking, a tie clip or lapel microphone is best. If wires are a problem, a wireless mike may do. Or maybe a directional microphone on the end of a fishpole can follow the performer or reach into a tree to catch the hoot of an owl. Shotgun microphones are excellent for rejecting extraneous noise, but may give unpredictable fidelity depending on other surfaces near the performer.
   
   
3. Use balanced lines, the kind with three wires and XLR plugs on the end. Unbalanced lines, one wire and a shield terminated with a phone or RCA plug pick up hum and other electrical interference easily, especially if the wires are longer than eight feet. Balanced lines, on the other hand, cancel out interference, transferring a clear and quiet signal over distances of 30 feet and more.
   
   
4. Bring adaptors and transformers. You never know what you are going to have to connect to what. Transformers will allow you to interface unbalanced equipment (ie. consumer tape recorders, CD players, and PA systems) with professional gear having XLR plugs. Radio Shack sells balancing transformers (part #274-016 or 017) for about $13. Higher quality varieties are available from professional audio distributors such as Shure of Evanston, Illinois and cost about $45.
   
   
5. Also use ground lifters and pads. Audio ground lifters permit your audio mixer to take a feed from someone else's mixer or PA system without picking up hum.
   
   Pads are resistors used in audio to reduce the strength of a signal. The powerful audio from a public address system, for instance, can be fed through a pad and reduced to a tiny voltage appropriate for a mixer's microphone input. Radio Shack sells pads or line attenuators (part number 274-300) for about $3.00.
   
   
6. Calibrate your VU meters. Send a test tone through your mixer and turn its volume and master controls up to about half way and look at your meter. Raise or lower both of them until the meter reads 0 VU. Then send the signal to your recorder and adjust its
   volume control to read 0 VU. Hopefully the VCR's control is not near 0 or the maximum on its scale; if it is, you need amplification or a pad, or maybe you've plugged the mixer's low level output into the VCR's hi level input or vice versa.
   
   
7. Always bring high quality headphones (with muffs to seal out ambient sound) and check the sound going into the mixer, and the sound going into the recorder. If the sound is good in one place and bad in another, at least you've narrowed down where to look for the trouble.
   
   
8. Always play back a sample recording before the actual recording begins, just to Murphy-proof your recording session.
   
   
9. If sound is being recorded separate from your video, place a visual and audible cue before the beginning of the recording that will permit the two to be easily synchronized. This is what filmmakers and some videographers use the famous "clapper" for at the beginning of each take. You can get the same result by holding up several fingers then clapping your hands in front of the camera.
   
   
10. Train your ear to listen for background sounds such as motors, wind, fans, whirring disk drives, audio hum or buzzing, buttons rattling against microphones, creaking mike cords, chirping crickets, distance traffic or voices, or the beep beep of wrist watches chiming out the hour. These sounds are much easier to silence when recording than to filter them out while editing.
    
    
11. Record sound. Shut everybody up and record a minute of ambient background sound of the room, factory, party, or forest where you happen to be recording. Not only can you use this as filler between prepared audio segments, but it also serves as nice background for voiceovers you might decide to add later.
    
    
12. Attempt to get the highest level signal possible without distorting your sound. VU meters should ride consistently around 0 dB with occasional spikes going up into the red" zone (+2, +4, +6 dB). This assures that your source sound is much louder than background hiss in your tape.
    
    
13. Use "manual" versus "auto" record levels. No machine can make decisions as wisely as you. Use automatic only when you don't have the fingers or time to twiddle the knobs.
    
    Pickup Patterns
    
    This has nothing to do with how men introduce themselves to ladies in bars. A Microphone's pickup pattern describes how well it listens in various directions.
    
    An omnidirectional microphone listens equally in all directions. You would use it to mike a crowd or a group of singers. It works well on a podium if your performers tend to move around or turn to the side while speaking, or lean forward into the microphone. Tie-clip microphones are generally omnidirectional, allowing the person's head to turn without affecting the volume of the sound very much. They also pick up chest vibrations to fortify the bass frequencies. Because tie-clip mikes are so close to the performer's mouth, they tend to pick up very little background sound.
    
    A unidirectional microphone listens in one direction primarily and rejects sounds from all other directions. A shotgun microphone is useful when you need to pick one member out of a crowd or one bird out of a tree (something my cats can do). The shotgun microphone must always be aimed to be affective; if the talent walks off axis, their voice will diminish abruptly.
    
    Directional microphones exhibit the proximity affect; if you get too close to the microphone, it boosts the bass in your voice thunderously. It also emphasizes the letters b, p, and t which sound like bombs bursting in air. Omnidirectional microphones don't manifest this problem until you are about an inch from them, but unidirectional microphones need to stay a foot or so from the speaker to avoid consonant bombardment.
    
    Part way between the omnidirectional and the unidirectional microphone is the cardioid and hyper-cardioid microphone. Here the pattern of sensitivity, if you graphed it, would be in the shape of a heart, representing great sensitivity at the tip of the heart (the direction the microphone is aiming), and almost no sensitivity at the heart's cleavage, usually the handle of the mike. Cardioids and their more directional brothers the hyper-cardioids are somewhat sensitive to popping p's and b's, and need to stay some distance from the speaker's lips to avoid the proximity affect. They are good, however, at reducing feedback, from PA systems where sound emanates from the speakers and works its way back to the microphone causing a whoop, squeal or ringing sound. Aiming the microphone and speakers away from each other and increasing the distance etween them also helps diminish feedback. Omnidirectional microphones are most sensitive to feedback.
    
    Bi-directional or figure-8 microphones listen in two directions, the front and the back and hardly at all from the sides. They are used primarily in talk shows and certain stereo applications.
    
    Pressure zone microphones, or PZM's, have a hemispheric pickup pattern listening omnidirectionally on one side of the microphone and not at all on the other. You would typically mount a PZM on a square of plexiglas or other flat surface. The mike would pick up all sounds on one side of the surface and ignore sounds on the other side. PZM mikes are often used on boardroom tables to pickup the voices of people around the table. The mike also tends to pick up the sounds of papers and pencils rattling. If your guests like to fidget, ask them to do it with their feet; the mike ignores sounds from its opposite side. Mikes with parabolic reflectors are handy for strengthening weak sounds such as woodland critters or distant outdoor conversations. Bass fidelity is poor (unless the reflector is huge) and the system easily picks up wind noise, as well as the snorts or sniffs of the person aiming the mike.
    
    Recording Stereo
    
    Naturally, you need a stereo camcorder or audio or video recorder to record stereo. Most of these machines will have two inputs marked CH1 and CH2 or L and R for the left and right channels. Some consumer gear display one audio input that accepts a stereo signal. The socket accepts a stereo plug that looks a little like a stereo headphone plug having a tip, ring, and sleeve construction. The tip carries one channel, the ring the other channel, and the sleeve the ground. If you have a stereo microphone with the proper plug, you are all set. If not, you will have to acquire an adapter with separate monaural left and right plugs at one end and the stereo plug at the other. Incidentally, if you hookup only the left channel, many camcorders and VCRs will switch to monaural and record the same signal on both channels.
    
    Note that if your tapes are played back through a garden variety RF modulator, the kind built into VCRs, usually tuned to channel 3 or 4, your stereo sound will turn monaural. This is true even if your TV set is stereo. To maintain stereo from the VCR to TV, you need to run the video and audio signals directly or employ a professional stereo RF modulator.
    
    Although there are stereo microphones with two transducers built into the same body, most professional stereo recordings are the product of two monaural mikes used independently. Typically you set a pair of microphones in the shape of a cross pointing one 45° to the left of center and the other 45° to the right of center. The heads of the microphones should be only a few inches apart to avoid accidental phase cancellation when the signal is played back monoaurally. Professionals call this arrangement X-Y or coincident pair miking.
    
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Another stereo miking technique is M-S or mid-side. Here, one mike, usually a cardioid, points directly forward towards the sound source. The second mike, positioned near the first, is bidirectional and listens directly to the left and right. The M-S technique requires special electronics to sort out the sound signals; you cannot simply plug the two microphones into a camcorder and get the desired effect. The special electronics subtracts some of the sound from one microphone from the sound of the other to create a very realistic stereo effect while reducing the chance of phase cancellation when the sound is played back monaurally.

What is phase cancellation? Whenever two microphones (used for stereo or not) pick up sound, and the mikes are any distance apart, sound will reach one mike before it reaches the other.

Certain frequencies of sound will have waves that are at their high point (compression of the air molecules) when they reach the first mike, while the trough between the waves (rarefaction of the air molecules) from the same sound is hitting the second microphone. In other words, the first microphone is vibrating inwards while the second one is vibrating outwards from the same sound. The two signals combine and equal zero, ergo phase cancellation. Your ear will hear a weak or hollow sound or a flanging science fiction-like whoosh to the sound. Whenever recording stereo, you must avoid phase cancelling situations, and check your monaural mix to assure your program sounds good on monaural TVs and public address systems.

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A third type of microphone is the stereo zoom mike, found on some camcorders and also available as an external mike. Set the zoom mike to wide angle and the side signals become stronger. When the mike zooms in to match the telephoto lens, the center signal becomes stronger reducing noise pickup from the sides, matching the picture.

Professionals using mixers or multi-track recorders are likely to use more than two mikes in a technique called close miking. Here each person or musical instrument gets its own mike and the mike is close enough to the sound source to pickup primarily that one sound. The sound engineer combines all the sounds and using a pan pot on the mixer (live or during editing) assigns that sound to the left or right channel or somewhere
inbetween.

Shotgunnery

The little grooves and holes that decorate a shotgun microphone's surface are not cosmetic but an integral part of its sound control system. You should never cover them with your hands, tape, or allow them to get clogged. If you do, the microphone's directionality and sound fidelity will be severely affected.

So how do you prevent the ports from filling up with rain, dust, or pollen without also blocking out the sound? Solutions:

1. Keep the mike fitted within its foam windscreen, even when it's in transit. This keeps the mike clean and protects it from physical shock.
   
   
2. When conditions are really messy, you can assure great sound reproduction by covering the microphone with an unlubricated latex condem. This is a techniques that was used by audio technicians during Operation Desert Storm to keep the desert dust from clogging the mike ports or interfering with the diaphragm (the part that vibrates when struck by sound waves).
   
   To install the condem, roll it onto the mike from the front pulling it tight almost to breaking. Secure it with gaffer tape or string below the XLR connector in the back.

This next tip will come as a surprise to you (like the last one didn't): Don't try to help a shotgun microphone do its job. The mike must have access to all of the sound, even the undesirable sound in order to properly reject it. If you try to pick up someone's voice through a window or from a vehicle or from around a corner, the undesirable "side" sounds won't be heard by the mike. If it cannot hear these sounds, it can't reject them and the mike's directionality will be diminished. Attaching a shotgun mike to the end of a pole works well because the microphone hears all of the ambient sounds, with no one nearby to block any of the sound.

Always remember to check for extraneous noise sources behind your performer. The shotgun microphone cannot ignore the ticking clock, an air conditioning fan, crowds or machinery noise behind the person speaking. It is best to position the mike so that unwanted noise is coming from the side where rejection is greatest.

Try not to move a shotgun mike around, or if you must, suspend it by a shock mount to soak up vibrations as you reaim the microphone. Every time a shotgun microphone is bumped, fondled, rubbed against anything, or its mike cord is pulled or twisted, a low thumping or rumbling sound will be evident.

To mitigate against some of this rumble, many shotguns today have a thumbwheel or switch that activates a high pass filter. The filter lets through high frequencies (voice etc.) while killing frequencies lower than 60 Hz. How long a shotgun is necessary? The short barreled shotguns work very well, especially with voice frequencies, but aren't very directional at low frequencies. The longer shotguns are directional at low frequencies as well as high.

Two situations where a shotgun microphone performs poorly:
In a very echoey room, sounds come from the performer, bounce off the walls, and hit the sides of the mike. In the process of rejecting these side sounds, the mike will cancel out the original sound resulting in a very weak or hollow sound. It is better here to use a cardioid mike.

When the mike must be used close to the perfomer, shotgun microphones are perhaps too sensitive, overboosting the bass or blasting you with volume when the performer happens to speak directly into the mike. Again, use a cardioid. What if you don't have a shotgun but need to do what a shotgun microphone does --- cancel out unwanted noise in an area. And let's assume that you cannot close mike your performer. This next trick is a little complicated and doesn't always work but is worth a try.

You need two identical microphones with identical, same length cables and a phase reverser, an XLR to XLR barrel connector having the two signal carrying wires reversed. (As a substitute for the phase reverser, you can always unsolder the signal wires and swap them in the XLR connector for this experiment, as long as you change them back to normal afterwards.)

Position one microphone so that it picks up mostly the noise and send its signal through the phase reversed cable. The second microphone should pick up the desired signal. The two mikes should be close together but would naturally be aimed in different directions so that one hears primarily the source while the other hears primarily the noise. Back in post, you start with your source sound and mix varying amounts of your noise" channel with it. Since the noise is out of phase, it will subtract from the noise picked up by the first mike, diminishing the noise overall. The process requires a little knob twiddling but the results may be very satisfying.

Power from the Phantom

There are two popular kinds of microphone transducers, dynamic and condenser. Dynamic microphones make their own signal directly from the vibrations of the sound. The signal may be a little weak, but plug them in and they work almost anywhere. Condenser microphones, on the other hand, usually make a stronger signal than their dynamic brothers but require power in order to work. The power may be a small battery inserted into the mike (preferably not a dead battery) or come from a separate power source at the end of the mike cord. Condenser microphones are a little more delicate than their dynamic brothers but they give excellent frequency response in a small light-weight package that is somewhat less sensitive to hum and other electrical interference. Shotgun microphones are usually condenser mikes. If the condenser mike does not have its own power supply, it must get juice from somewhere. Professional camcorders and audio mixers usually provide phantom power to these mikes by throwing a switch. Be sure to feed phantom power to microphones that are designed for it; you could accidentally toast your dynamic mike.

If your mike cables have to be more than 100 feet in length, you will probably find dynamic mikes too weak to produce an adequate signal. Condenser mikes will usually do the job and so will N/Dym dynamic mikes. The output levels of N/Dym mikes is at least 10 dB higher than many standard dynamic mikes. Electro- Voice and Shure both offer N/Dyms.

The Timeless Wireless

Wireless mikes are handy in the field because you can clip a mike to a performer's lapel then move the camera wherever you like. There are no fishpoles or shotguns to aim and the close miking rejects noise and echoes pretty well.

UHF wireless microphones are most expensive but work the best because they use relatively "quiet" transmission frequencies.

Of the VHF microphones, the diversity mikes are good because there are two receivers listening to the mike transmitter at all times. If for some reason one of the receivers gets a weak signal, the other one may still be getting a strong signal and will take over.

Next down the line is your standard single receiver wireless microphone. It runs the risk of having a hissing sound or occasional audio dropouts as the performer moves close to metal, moves behind a conductor (a desk or a person) or travels out of range. VHF wireless microphones all suffer from interference from taxi radios, other mikes, and remote controlled devices. The better models put out powerful signals that override these interferring signals. Some models have switchable frequencies allowing you to avoid a noisy transmission channel. Some of the better models have companding, the method of compressing the dynamic range (the ratio between weak sounds and strong sounds) of the original signal into a smaller more easily transmitted range, and at the receiver, expanding the compressed signal back to normal reestablishing the original dynamic range. Also the better wireless mikes have input limiters that reduce the strength of loud sounds to keep the transmitter from being overloaded. Thus the talent can let out a scream without blowing you off the air.

Miscellaneous Tips

Echoes can be a problem when you are shooting indoors, indoors, indoors. One way to quell sound reflection is to hang shipping blankets like the ones you buy at U-Haul on any walls that won't appear in your picture. Not only will this reduce echoes, but it will remove the occasional hollow sound that you get from accidental phase cancellation when sound bounces off a wall and hits the microphone in competition with the original
sound. These blankets can also be draped in a U shape behind the microphone (unless you are using a shotgun mike) to reduce noise and echoes from that direction.

Gather the blankets so that they are not flat or else they will reduce only the high frequency reflections creating a"tubby" sound. Better than blankets is Sonex, squares of egg crate-like foam material that reduces both high and low frequencies.

Clip on mikes have a tendency to pick up clunking and scraping sounds from the talent's jewelry, accessories, or fabrics. Train your ear to catch these sounds before the shoot
begins. You can tape or pin jewelry, scarves, sweaters, and any loose clothing that is likely to come into contact with the mike itself. Use small pieces of gaffer's tape to secure the cable so that it doesn't rattle or tangle. Taping the cable also prevents the mike from being pulled out of position as the performer moves, and also keeps the wire away from the talent's nervous fidgeting hands. Secure a wireless mike antenna as well. Beware that many fabrics are not transparent to sound; always check to see if your audio is muffled. If so, try to poke the head of the mike through a crevice in the fabric so that it has a clear shot to the outside.

Some silky fabrics cause static electricity, adding snap and crackle to your sound. Bring along anti-static spray and give a good dose to the fabric around the microphone area. Sometimes you cannot find a good place to attach a tie-clip microphone. Try this: remove the tie-clip and roll a layer of double-sided foam tape, the kind used to temporarily mount artwork, around the mike. Then stick the mike wherever convenient.

Take good notes when shooting. Indicate what microphones or filters were used. Your tapes may come from everywhere, under broadly different recording conditions. If they have to be mixed, you will want your sound to remain consistent, which means some sounds may have to be equalized or enhanced in order to match other sounds. Your notes will remove some guesswork. Avoid drastic equalization during the recording phase
leaving this step for post. Once a sound is boosted or your tape has saturated or overloaded, it's nearly impossible to undo the damage. Record most of your work "flat" and save your processing for later.

Favorite mikes: The $300 Sennheiser 421 with a good pop filter has a meaty bass and a smooth high end without nasty peaks. The Shure SM-7 and Electrovoice RE-20 are also good all around mikes, especially for voices.