The Selection and Use of Shotgun Microphones on the Set

Utilize the Hierarchy of Microphone Techniques

by Fred Ginsburg C.A.S. Ph.D. MBKS

When a production sound mixer eyeballs a scene, we strategize how we are going to capture all of the ensuing dialogue. In our head, there is a basic game plan to follow as we evaluate the blocking of the shot. This “Hierarchy of Microphone Techniques” consists of the following:

  1. Overhead boom.
  2. Boom from underneath.
  3. Boom mics as plant mics.
  4. Lavalier mics as plant mics.
  5. Lavalier mics as body mics.
  6. Lavalier mics, wireless.

Overhead miking from a fishpole (or studio boom) is the most favored technique for film/video production and is the best choice most of the time.

Using a boom mic yields realistic perspective; and a natural blend of dialogue and sound effects (footsteps, hand prop noise, etc.)  In contrast, body-worn lavaliers only provide a constant perspective (close-up sound) and may not pick up the other sound textures in the scene.

Another advantage of overhead shotgun miking is that it is much easier to capture dialogue from multiple actors in the scene. Two-shots, three-shots, no problem. When I used to mix episodes from a police drama, it was not uncommon for the camera to pan across a squad room full of officers. But with just one (sometimes two) boom mics, we could cover over twenty cast members!

The operational word here is “overhead”. Why?

There is a tendency for filmmakers to rely too heavily on their camera mounted shotgun mics rather than separately mounted boom mics. Obviously, having a microphone on the camera is more convenient. But our objective in the field is not convenience, but obtaining the highest quality sound possible!

Think of your shotgun microphone as a telephoto camera lens. A long lens will isolate and magnify a distant subject, but at the same time it will compress the perceived distance between subject and background. Everything appears to be closer together than they physically are.

The same sort of spatial compression takes place with microphones. The voice of the subject will sound closer, but any noise in the background will also be magnified.

Therefore, the key to isolating voice without background noise is to create a line of sight with the microphone that sees the voice but does not see the background!

To put this in cowboy talk, aim the mic from ABOVE the subject so that the mic points DOWNWARD. The line of sight reaches from the front of the mic, to the mouth, and then towards the ground. Background noise and ambiance will strike the sides of the microphone (which is the maximum rejection angle) rather than striking the mic along its most sensitive front axis.

In the event that it is impossible to mike from above, the next best option is to mike from below, so that the line of sight terminates with sky. Miking upwards tends to emphasize bass a bit more, since the mic is seeing more of the chest cavity along with hearing more bass reflections from the ground.

Be careful, as many camera operators are not as accustomed to maintaining a strict lower frame line as they are at watching their headroom, so the mic tends to pop into the shot more frequently.

Another important consideration when booming is not just the angle of the mic but the distance. Shotgun mics are not designed to be used (for broadcast quality sound) at much more than a few feet. One of the great advantages of using the mic on a fishpole, as opposed to being attached atop a camera, is that the mic can be brought close to the subject even when the camera isn’t.

I often tell novice boom operators that they aren’t doing their job properly if the camera operator fails to complain that the mic is in the frame (during rehearsal). Every inch closer that the mic can be to the subject will improve the quality of the sound. Never fly the mic higher than it absolutely needs to be if you want to control echo and background noise. Several inches to a foot over the top of talent’s head is ideal; up to a few feet overhead is okay depending on the situation.

Place a thin strip of white tape on the tip of your boom mic’s windscreen to make it obvious in the camera viewfinder. Better for the operator to notice it on the set than for the editor to discover it lurking in the frame during screenings! To achieve the closest mic placement, always begin with the mic clearly visible in the frame, and then move it outward gradually until it clears the viewfinder. Had you started with the mic placed way out of frame, and gradually moved closer – the camera operator would probably have panicked and instructed you to stop way far above the frameline.

Some camera operators confuse width with height. A wide-angle lens means wide from left to right; it doesn’t mean that they have to reveal several feet of air above the talent’s head. A simple tilt-down of the lens will correct excessive headroom in the composition when using a wide angle lens!

Learn to recognize and take advantage of the on-axis (live) and off-axis (deader) angles of your mics. Most shotgun mics are very much on-axis at the front (say, twelve o’clock), and taper off towards the back (six o’clock). But at exactly six o’clock, there is an increase of sensitivity! In other words, the back of the mic does not offer the most rejection to background noise. The most rejection occurs around four o’clock and eight o’clock respectively.

So to decrease a source of noise, you would not want the mic facing directly away from it, as that would only serve to put the noise at the live spot in the back. Instead, angle the mic so that the noise source strikes slightly to the side and rear.

When deploying your mic overhead, keep these angles in mind. Often it is better to compromise the angle of the voice (slightly) in order to keep heavy background noise to a minimum. Any angle of the mic should be consistent with the source of the worst noise. For instance, a person talking on the sidewalk would put the mic overhead, but cheated towards the buildings and away from traffic — even if the camera changes shot angles.

Similarly, a subject walking along the edge of the surf on a beach should have the mic facing inland, not out towards the noisy surf.

Another important factor to pay attention to is “perspective”. What the audience sees should more or less agree with what the audience hears. Note that there is a distinct difference between “distant” shots and “wide shots”.

The distance between microphone and subject should agree with the distance to the screen or camera. In a distant shot, it is natural for the voice to sound farther away and for there to be a greater presence of ambiance. Close-up angles should consist of more voice and less background.

Be careful that when the camera merely changes its angle, that you maintain the same dialogue volume for your actors. Close-ups should NOT sound louder than medium shots! Just because the boom mic can get closer to the actor when you shoot the close-up, the mixer should reduce the volume settings to compensate. The key difference between the sound of a close-up versus the sound of a wider (medium) shot is that close-ups are mostly voice with minimal background; and wider shots are a blend of voice with some background. But the volume of the voice remains fairly consistent.

If, however, an actor walks away from the camera (creates more distance from the audience), it would be natural for the volume to taper off.

Angle of motion is very important in terms of maintaining perspective. A person walking away from the camera should not be moving towards the microphone, nor vice versa! Novice boom operators are notorious for perching themselves in a safe spot out of the frame (such as a step ladder off to the side of the set) that places the mic in a position not consistent with the direction of travel relative to the lens.

A person with their back to camera should not be facing the boom mic. A person walking up to the camera should not be walking away from the boom mic.

I should point out, though, that when we do advanced miking, we often deploy secondary “plant mics” that actually may be facing talent as they walk away from the camera. Audio from those mics are carefully blended in so that the “away” dialogue is clear and audible, but subtle enough to be consistent with the illusion of perspective.

To balance a strong voice against a weak voice, use your mic angle and placement rather than riding gain (volume) on your mixer/recorder. Let the strong voice strike the mic slightly off-axis and/or from a little more distance than the softer speaking actor. This will balance the relative volume of both people without having the background noise continually changing during the shot.

Let’s examine the types of microphones we have to choose from.

Microphones can be defined by two sets of parameters: sensitivity and pattern.

In terms of sensitivity, there are three main classes that a microphone can fall into.

Dynamic: Think of a dynamic microphone as a manual typewriter. The harder that your finger hits the key, the stronger the imprint. With a dynamic mic, the pressure of the sound waves moving the diaphragm actually generates electrical current (which is what the sound signal is). Dynamic mics are extremely rugged and do not require any form of battery powering. They are relatively insensitive to background noise (or feedback) and are commonly used as handheld performance mics and reporter’s mics.

A dynamic mic deployed close to the mouth will reject all but the loudest background noise, making them ideal for stand-up reporting (where the mic can be seen on camera) or narration recording (to eliminate as much background as possible).

Dynamic mics tend to naturally compress loud noises, making them a good choice for recording explosive and crashing sound effects. A loud sound effect, unless carefully recorded, will tend to be “blown” right off of the recording tape, which is why real gunshots that leave your ears ringing only sound like dull pops on video.

The downside to dynamic microphones is that they have very poor reach in terms of distance when it comes to dialogue. They are pretty much useless on a boom or fishpole.

Here’s a tip: When filming an actor who is pretending to be a performer and will be seen using a handheld mic, it is much safer to consider the hand mic as merely a stage prop and to mic the actor with a boom or lavalier. Actors in those situations tend to gesture wildly with the mic, making your chances of getting good dialogue quite slim.

The next most sensitive group of microphones are the electret condensers. Electret condenser microphones are like electric typewriters. These microphones operate off of a nominal voltage (usually 1.5 volts) which is derived from an internal battery such as an AA or button battery. The voltage that creates the audio signal comes from the battery (as opposed to being generated from scratch, as in the case of dynamics). The relative sound levels control the capacitance, discharging voltage according to what the mic hears. Almost think of it like a meter that measures the sound, and releases a signal accordingly.

Electret condenser mics offer much more sensitivity (range) than dynamics, and include what is commonly referred to as “ENG” grade shotgun mics as well as most lavaliers. They are nicknamed for their popular role in news gathering.

Good electret condenser shotgun mics are often advertised as “video mics” and range in price from a couple hundred dollars on up. Most of the major microphone manufacturers offer a decent “short shotgun” for videographers and low budget filmmakers. Make sure that you purchase a balanced XLR mic; avoid the prosumer models that only have unbalanced mini connectors.

The third class of professional microphones are the true condenser type. If the other classes of microphones represent manual and electic typewriters, then think of electronic word processors.

Condenser shotgun mics are the most sensitive and offer the greatest working range for Production. Condenser mics require external powering such as 12volt T or 48volt Phantom, which can be supplied by an accessory battery power supply plugged in line between the microphone and the mixer/recorder. Most mixing panels, digital recorders, and better camcorders offer XLR mic connections with 48v Phantom powering.

Consumer units, equipped only with mini connectors, do NOT provide Phantom powering. What those devices refer to as “remote mic powering” is merely a couple of volts intended to power the (manufacturer’s own) inexpensive electret condenser stick mics via the mini connector.

Condenser shotgun microphones are considerably more expensive than ENG mics, but are worth the extra expense. Their superior range and quality make them the standard for feature film production, episodic television, commercials, and other major production.

A note here on microphone powering, which is an area very confusing to many people. As stated before, dynamic mics do not require any external powering, and plug directly into the MIC INPUT of a mixer/recorder. Electret condenser mics are self-powered (by an internal battery) and also plug directly into the MIC INPUT. Some electret condenser mics CAN be powered by Phantom powering instead of a battery, as a matter of convenience. Just because a mic can work from Phantom power does NOT make it a true condenser microphone.

Condenser mics require external powering, which can be derived from the recorder/mixer, OR a battery powered 48vPhantom supply located anywhere along the mic cable path. For instance, the mic connects to a regular XLR cable, that cable plugs into the power supply, and then another short cable connects the power supply to the MIC INPUT of the recorder.

In the instance that a microphone does not require power at all (dynamic), or if the mic works off an internal battery (electret condenser), or an external 48vPhantom power supply is used inline – then do not use the 48vPhantom powering option found on the portable recorder/camcorder. Note that leaving the remote power setting ON will not hurt the mic, but is a waste of battery resources.

The other parameter by which we classify shotgun mics is by the pickup pattern.

Omnidirectional refers to hearing equally well in all directions. Most lavaliers are omni, which is good since they could end up being worn in different places and at different angles in order to accommodate clothing styles. Omni mics are also preferred for handheld interviews, since this allows for the unexpected overlapping of dialogue between interviewer and subject.

Cardioid pattern literally means heart shaped, and refers to microphones that are more directional from the front.

Hypercardioid or supercardioid are considerably directional. This group includes what are known as “short shotguns”.

Ultra-directional means extremely directional, such as full or long shotgun mics.

So which mic to use?

The rule of thumb is that the more directional the microphone, the greater the front reach (and better side noise rejection), but the more it will emphasize echo in a small room. Therefore, reach the best compromise between the reach you need and the mellowness you would like to hear.

Long shotguns work the best for most exterior shots, since theses mics are characterized by long reach and very narrow pick-up. The narrow field of view helps to control background noise if the mic is deployed overhead. The greater range helps because exterior shots are very often much wider than interior frames, since there is more interesting stuff to look at or action to cover.

Long shotguns can be successfully deployed up to 8 or 9 feet overhead, depending on the situation. Of course, better results will always be had if you can move the mic closer to talent; especially if you are fighting a lot of background noise.

Although long shotguns tend to exaggerate echo in a confined room, that is normally not a consideration outdoors. Instead, ambient noise is generally the problem, and the long shotguns do the best job of defending against it.

Always used a blimp windscreen on your long shotguns to guard against “contact” wind noise (wind striking the microphone element). I find that using a thin foam windscreen inside of the blimp (but still leaving some airspace) gives almost twice the protection. On the very sensitive condenser mics, a furry windsock will help to disperse the wind and diffuse it upon impact.

To guard against rain, use lots of ScotchGuard spray. Extreme rain (or fire fighting) would call for a thin condom over the mic itself, as well as a rainhat over the blimp made from what we call “hogs hair” or “rubberized hair”. Hogs hair is a thicket type material that will break up the raindrops and prevent the pitter patter sound of them striking the windscreen, roof of a vehicle, or roof of a recording stage.

Long shotguns may also be used on some interiors, providing that the room or sound stage is very large and free of echo. They offer the advantage of increased overhead range and headroom on wide shots. Their disadvantage on interiors is: (1) they are physically longer and may bump a low ceiling; (2) they must be precisely cued or aimed because of their narrow pattern [to cover two actors requires a very good boom operator]; and (3) long shotguns will exaggerate room echo.

Interior locations are usually better off being miked with a short shotgun. The short shotgun features a slightly wider pattern and slightly less range, but does not exaggerate the room echo as much. The wider pattern and physically shorter length of theses mics facilitates use with lower ceilings, especially when it comes to covering multiple actors. Condenser short shotguns can be deployed indoors up to 5 feet above the actors (though 2 to 3 feet is better).

Indoors, all short shotgun mics should always be used with a foam windscreen. Out of doors, a blimp windscreen or a furry style slip-on windscreen should be used.

In a pinch, simply wrap a few layers of cheesecloth over the foam windscreen, and then cover in a tube-style sweat sock. It works.

Any shotgun mic should always be used in a good shockmount to eliminate handling noise and vibration. The plastic mic clamps that come in the box should stay in the box! Any good shotgun mic requires some sort of isolating suspension.

In addition to the long shotgun and short shotgun, Hollywood has begun using a third type of microphone in its quest for perfect dialogue. Some condenser cardioid microphones have become popular for their ability to reduce or even eliminate echo in a small room or set!

These “wide pickup angle” full condenser cardioid mics yield a very rich voice track, are favored for close-ups and medium close-ups where the overhead mic will not be more than two feet overhead. Their wide pickup patterns make them unsuited for long reach; the dialogue would be too thin compared to room ambiance. But deployed at relatively short distances (under two feet), they do an amazing job of removing echo. Perfect for small bathrooms, kitchens, and hard-walled living rooms. Not to mention spartan offices, marbled lobbies, and gymnasiums.

One final point. Make sure that the boom operator can HEAR the soundtrack! In order to properly position a mic both in terms of distance and angle, the boom person must be able to listen to what is being picked up. Provide a headphone feed either via a wireless (assistive listening) rig or with a long headphone extension cable taped to the mic cable.

On professional sets, we utilize a special mic cable (known as a “duplex cable” or “boom cable”) that combines an XLR  microphone cable with a headphone cable in one housing. This cable conveys the audio signal from the mic to the mixing board while sending a headphone feed back to the boom person.

Because there are often multiple mics in use on a set (boom, plant, lavalier, wireless) — the boom operator should be monitoring the entire mix (not just the boom mic).  The boom operator needs to be aware of any phasing problems that would be created by two mics picking up the same actor at the same time. If the boom person can only hear the boom microphone, he or she would remain unaware of the fact that another mic (such as a lavalier or plant mic) could be in play. The boom person would end up over-compensating and trying to capture too much of the scene, unaware that some of the dialogue was covered by other mics. Unless the boom mic were on its own separate audio track, the resulting audio would be very hollow and reverberant due to the conflict of having two open mics hearing the same audio.

Fred Ginsburg, C.A.S., Ph.D., MBKS is a specialist in production sound recording for motion pictures and video. His background includes nearly two decades as a sound mixer on feature films, episodic television, commercials, as well as corporate and government. Author of over one hundred technical articles and one textbook, Fred is currently an Adjunct Professor at California State University Northridge, and has lectured and instructed workshops about location sound recording at universities, studios, law enforcement, and production facilities across the United States and internationally. When not involved in filmmaking, Fred’s passion for shotguns extends to the 12 gauge variety, where he dons historically correct Western attire and competes in the sport of Cowboy Action Shooting.

Featured in StudentFilmmakers Magazine, April 2009 Edition.
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