AUDIO FOR VIDEO - PART 2 (MICROPHONES & TECHNIQUES)
By Hal Robertson
There are very few things that sound worse than the built-in microphone included with most camcorders. These mics seem to pick up more background noise than good sound. Apparently, manufacturers think buyers don't care because built-in microphones haven't changed much in 10 years. What's worse, several camcorders today don't even have a jack to plug in an external microphone! By using an external microphone to record your sound, you can dramatically improve audio quality while adding professionalism to your videos.
In this article we will explore the various types of microphones available for video production and different techniques for using them.
All microphones have two determining characteristics: Pickup pattern and operating principle. The pickup pattern determines from what direction the microphone will capture sound. For the sake of simplicity, we will discuss the two most common patterns: Directional (or "Cardioid") and Non-directional (or "Omni-directional). The name "cardioid" comes from the shape of the pickup pattern on a directional microphone - it vaguely resembles an upside-down heart. Sounds at the front of the microphone are predominant, sounds at the sides of the microphone are much lower in volume and sounds at the rear of the microphone are barely picked up. Non-directional microphones pick up sound evenly from all directions.
Operating principle refers to the electrical method used to pick up sound - and is divided into two categories: Dynamic and Condenser. Dynamic microphones use a sort of "backward speaker" method to obtain sound. A small diaphragm is attached to a coil of hair-thin wire suspended in a magnetic field. Sound pressure hits the diaphragm, vibrating the coil of wire in the magnetic field, producing an electrical signal (didn't we do something like this in Jr. High science?). In turn, this electrical signal is attached to your camera and recorded on your videotape. A condenser microphone uses an even smaller diaphragm attached to a capacitor. The output from this capacitor is a very small electrical signal. Because it is so weak, it must be amplified before attaching to the mic input of your camera. The amplification is built into the microphone, but requires electricity in the form of a battery or by "phantom power" supplied through the mic cable from the camera or a microphone mixer (professional mics only). Because the condenser diaphragm is so small, less acoustic energy is required to make it vibrate. This is why most condenser microphones are more sensitive or "hotter" than their dynamic cousins.
Many types of microphones are available, but which ones are best for video production? Video microphones fall into three categories: Handheld, Lapel and Boom microphones. Each has its benefits and will be suitable in different applications.
The on-the-scene news reporter typifies how handheld microphones are used. A television reporter stands on-camera holding a microphone about chest high. If they are interviewing someone, the mic is passed back and forth between the two. This is probably the least professional way to gather sound but it is fast, easy and works every time. The disadvantage is that the microphone is clearly visible and susceptible to handling noise and wind noise. You must also rely on the talent to get the mic in the right position to pick up sound. However, if you need to provide a sense of urgency for your next video, a handheld microphone is just the ticket. It lends a certain "live" look and implies spontaneity.
Also known as "lavaliere" mics, these miniature microphones are usually worn on clothing - clipped to a shirt, jacket or tie. They can also be worn under clothing or a tie, but that will almost certainly muffle the sound. Lapel mics are the workhorse of the news industry. Tune into any news program and, if you look long enough, you will see one or maybe two lapel mics clipped to the talent (networks are paranoid and can easily afford to use a backup mic). These microphones are typically very small (some are smaller than a pencil eraser) and are easily concealed in clothing. In theatrical applications they are often woven into hair or taped to the side of a face, with just enough sticking out to obtain good sound. As a rule, lapel microphones are non-directional and pick up sound from all directions. Although directional lapel mics are available, they are generally larger, more expensive and very prone to mechanical noise (brushing against clothing, etc.). The obvious advantage to a lapel mic is that it is always the same distance from the subject's mouth. The primary disadvantage is, being non-directional, they aren't always useful outdoors and are easily swamped by loud background noises (machinery, vehicles, wind, etc).
The name "boom" actually comes from the stand that holds these microphones. The microphones themselves are a highly directional type called a "shotgun mic". A boom is a special microphone stand that allows the mic to be hung over the subject(s) on camera. To keep the microphone out of the shot, these stands can be adjusted for height and angle. In addition, the microphone can be swiveled 300+ degrees to pick up sound from any subject. You can see these boom stands sometimes on "The Late Show" or "The Tonight Show" when they take a wide shot of the stage. The producers of "Home Improvement" have used a boom mic as a prop several times. The portable version of a boom stand is called a "fish pole". You can see these at news conferences and when reporters are chasing people down the street. In my opinion, the boom mic is the ultimate way to capture sound for video. Because they are highly directional, they pick up very little background noise - they are not held by or attached to the talent, so there is a minimum of mechanical noise plus, they sound great! The only disadvantages are that they must be carefully positioned just outside the video frame and, if movement is required, you will have to bring another helper to the shoot.
One last type of microphone that falls outside convention - the boundary microphone. Originally manufactured by Crown under the trade name "PZM" (pressure zone microphone), now everybody makes one, including Radio Shack. The boundary mic is unconventional in that it lays on a table, floor or wall and effectively uses the entire surface for pickup. The larger the surface, the better the sound. By positioning the microphone element a fraction of an inch above the surface, the boundary mic eliminates phase cancellation and other strange things that happen to regular microphones. Boundary microphones excel at picking up large groups of people, background ambience and crowd noises (applause, laughter, etc.). On the other hand, they also excel at picking up air conditioning rumble, creaking doors and bystanders. While you can't use them in every situation, they are handy for corporate board meetings and video depositions. Just lay one or two microphones on the conference table and start recording. Just don't allow anyone to lay books or papers on your mics! You must experience this to believe it.
TIPS AND TECHNIQUES:
For some reason, most news agencies choose to use non-directional models when they need a handheld microphone. Specifically, a 30+ year old design from ElectroVoice - Model 635 (the ElectroVoice RE50 is also popular). The 635 is small and easy to handle, but it picks up gobs of wind noise and mechanical noise and really doesn't sound very good (it also produces hum around computer monitors). Don't ask me why this is the microphone of choice, I've never liked it and prefer to use directional mics. There are many directional handheld microphones to choose from, but the industry standard is the Shure SM-58. The SM-58 is built like a tank and legendary in professional sound circles.
Whatever handheld mic you use, mechanical noise can be an problem. This is noise generated by actually handling the microphone. Some mics pick up very little of this noise (ElectroVoice N-DYM series for example) while others are nearly unusable. A couple of years ago, I shot a quick demo video for a stand-up comedian. It was a very intimate setting, but he still wanted to use a handheld microphone. He told me he could use the club's mic, so I didn't bring one. Unfortunately, I also neglected to bring my monitor headphones (what was I thinking?!). The resulting video was almost worthless due to the clunking and banging sounds made by the club's microphone. The moral of the story is to choose a handheld microphone with very low handling noise (and always bring your headphones to the shoot). This is not something they list on the spec sheet, so plug a few in and try them first.
Because they are typically non-directional and unusually small, lapel microphones are very flexible and useful. One common problem with handheld mics is that the sound changes when the position of the mic changes. A lapel microphone quickly solves this problem by keeping the mic at a consistent distance to the talent. Not only consistent, but also close - usually 12" or so from the mouth. This helps when controlling several subjects in a group, such as a newscast or interview setting. Because the each microphone is so close to it's subject, you can easily blend the voices with a mic mixer - matching each microphone's level to the others in the group. The perennial favorite lapel mic for news is the Sony ECM-77. Some other favorites are the Sennheiser MKE-2 and AKG C417. My personal favorite is the Shure WL-93 - a flat, miniscule microphone that sounds very open and natural.
There are a few things to remember when choosing and using a lapel microphone. First, virtually all lapel mics are condensers, which means they require electricity in one form or another. Always pack spare batteries for the shoot and keep a couple in your desk drawer if you have a studio. Some lapel mics use bizarre (and hard to find) battery types, so make sure you have the right kind on hand (I dare you to find an "N" cell after Radio Shack closes). You might also invest in a small multimeter to test batteries. RS#22-802 is an excellent choice that folds up small enough to fit in a camera case or shirt pocket. Second is what I call the "umbilical cord" factor. If you are shooting testimonials or FYI segments, you must deal with average citizens. These folks are not used to "wearing a wire" and will inevitably try to get up and go get another cup of coffee while still attached to your camera or mixer! You can minimize this hazard by making them aware of the problem while you are clipping the mic on. Offer to detach them whenever there is a break in the shoot. Of course, if you use wireless lapel microphones there is no problem, plus you can get some neat sound effects when they go to the bathroom.
Regardless of which mic you choose, if you are shooting outdoors you will need a windscreen. These are usually made of open-cell urethane foam and are available in many colors (darker colors are best for video). You should buy windscreens for all your handheld and lapel mics. Not only do they cut wind noise outdoors, they will also keep your talent from popping the microphone with breath noises (called "plosives" like "B", "P" and "T"). Keep in mind, foam windscreens will deteriorate over time and should be replaced regularly for this and other sanitary reasons.
As I mentioned, my favorite method for audio pickup is the boom or shotgun mic. With no handling noise, no umbilical cord problems and no on-camera visibility, this is the clear winner for me. Shotgun mics come in many forms from many manufacturers. Beyerdynamic, Sennheiser and Sony all make excellent "short shotguns" optimized for film and video production. I have personally spent many happy hours with the Audio Technica AT-815. Each of these microphones provides high quality sound, various options for mounting and operation, and most come with a foam windscreen. When mounting to a boom or fishpole, you must use some type of "shock mount". This is a special microphone clip that is suspended by elastic or rubber straps to eliminate mechanical noise transferred through the pole. This shock mount is not usually supplied with the microphone, so you get to spend another $100 or so. Whether you use a boom operator (highly recommended) or not, make sure there are headphones available to monitor the sound of the microphone prior to and during the shoot. Due to the highly directional nature of shotgun microphones, monitoring the mic will ensure the highest quality sound.
If you choose wisely and listen before you buy, you can achieve high quality video sound with minimal expense. Unfortunately, there are few stores specializing in video sound so you will probably be visiting music and electronics stores. If you don't trust your ears, take an assistant along to listen to different microphones. Or alternatively, take your camera, attach each microphone candidate and record a segment or two for later examination.