To appreciate where we are in regards to microphones, let’s review a little history.
By the late 19th century, legendary inventor Thomas Edison experimented with the idea of adding sound to moving pictures. One famous 17-second film clip shows Edison's assistant playing a violin in front of an enormous horizontal cone. That cone etched the sound onto a foil covered cylinder, which would later be synchronized to the film playback via a series of pulleys and belts.
That primitive cone performed the same function as the most sophisticated microphone in use today by transforming sound waves into a medium to be used with motion pictures (or video in our case). Thankfully, we don't have to go shopping for the latest cone, as technology has grown to the point where a variety of mics are available to the videographer, specially designed for a myriad of tasks. This guide is designed to provide you with the information needed to make a decision that best suits your needs and budget.
Depending on their intended use, microphones have a variety of "pickup patterns" or the directional characteristics for different intended uses. There are two basic types:
- Omnidirectional. This pattern is equally sensitive to sound in all directions (hence the name omni). The most common type, omnidirectional patterns are frequently used with handheld or "stick" mics, lavaliere or "lapel" mics, and boundary (PZM) mics. The "pickup pattern" of an omnidirectional mic resembles a large invisible ball. Because the pickup pattern is sensitive to sound from all directions, it may sometimes allow unwanted audio along with the desired sound.
- Unidirectional. As the name implies, these mics accept sound from primarily a single direction. Highly discriminating, these mics concentrate their pickup pattern on a relatively narrow path, rejecting sound outside this area. Usually called a "boom" or "shotgun" mic, most high quality TV shows hang these unidirectional mics on a pole pointed directly at the actors as they speak. Shotgun mics are also available for the home user and are ideal for plays, speeches and other locations where precise sound is required.
- Cardioid. Lying somewhere between an omni and a unidirectional pattern is the heart-shaped cardioid pattern. This pattern is often found with studio mics along with other vocal handheld mics. You may also find variants of this pattern, described as super-cardioid or hyper-cardioid, used in short shotgun style designs.
Balanced or Unbalanced?
A balanced cable has three wires. The first is the ground and the second and third carry the identical signal, although out of phase. The receiving device, a camera or mixer, interprets the two signals and corrects for any interference.
An unbalanced mic only has two wires, one is the ground and the other carries the signal. This setup is more susceptible to RF interference. This doesn't mean the quality is less, but all things equal, an unbalanced mic will have less protection from outside interference than a balanced one. Often, these mic cables have an 1/8″ connector such as a stereo minijack. Adapters can be purchased to connect an unbalanced cable to a balanced one and vice versa. As a general rule, if you need to run a cable longer than thirty feet, you should use balanced cables. The longer the unbalanced cable is run, the more chance of interference.
Mics don't always need an internal battery to operate efficiently. Some mics don't need any power at all or require Phantom power supplied by the camera or a mixer. Camera mounted shotgun microphones usually use phantom power..
Many mics do use internal power to process the sound the microphone receives. Usually a small battery like an AA or a 9-volt is sufficient to power the mic for an extended period of time. Many shotgun mics require batteries as do all wireless mics..
Most consumer cameras will not provide phantom power while higher-end prosumer cameras might. Check your user manual for guidance. If your system is battery powered, always carry plenty of extras and use fresh ones before your clean audio starts to degrade in quality.
Look, Ma…No Wires!
Being free from the constraints of an audio wire plugged into your camera provides a whole new range of creative possibilities. Luckily, better wireless systems have come onto the market with capabilities that were beyond the reach of all but the most well funded production houses.
While not new, wireless systems have experienced a huge leap in capabilities. Smaller, cheaper and more powerful, wireless transmitters and receivers experience less of the frustrating "drop outs" and static of a few years ago. Today, diversity and true diversity systems have replaced the "drooping antenna" system of old.
How a wireless system processes the signal it receives from the transmitter can be the difference between hearing the groom say, "I do" or hearing nothing. Many wireless systems utilize two methods of processing received signals, diversity and true diversity.
Simply put, a wireless mic with diversity will have a receiver with two independent antennas. The receiver will constantly compare the signal being received by each antenna and seamlessly switch between them to maintain the strongest signal at all times.
Some systems may employ a True Diversity method. This system uses two independent receivers (both getting the same signal) as opposed to two antennas feeding one receiver in the diversity system. The strongest receiver signal is "chosen" and fed to the camera for recording.
A "body pack" transmitter is about the size of a deck of cards and usually has a permanently connected lapel mic with about 2-3 feet of wire. It clips to a belt or waistband and must usually be hidden either behind the back or under clothing.
You can even turn most handhelds with XLR connections into wireless mics. Simply use a wireless transmitter that plugs directly into your handheld and you are free to roam.
Receivers are usually mounted on the camera. Some provide for mounting on the accessory shoe on top of the carrying handle while others use industrial hook and loop fasteners to attach the box to the battery or camera body.
VHF or UHF?
Wireless mics are available in two frequencies, Very High Frequency and Ultra High Frequency, each having numerous channels in each. The VHF spectrum is limited by law to a maximum output of 50 milliwatts of energy. Most VHF transmitters put out the maximum power allowed to achieve maximum range and maintain a reasonable battery life. Use VHF if cost is an issue or you are in an area of little or no interference.
UHF systems can transmit up to 250 milliwatts of energy, maximizing range and minimizing dropouts, but at the expense of battery life as the extra energy is required to maintain this much "horsepower." Should your requirements be stringent or you know you'll be in an area of strong interference then a UHF system may be the answer.
Once your perfect mic has been chosen, you'll notice a great improvement in the quality of every production. Thomas Edison had the right idea more than 100 years ago; now imagine what he could have done with something better than a cone!
Randy Hansen is a TV news chief photographer and uses at least four different mics on a daily basis.