Buyer's Guide: Microphones

Production audio is like fish stored in the refrigerator. The best audio is like fresh fish; you don't notice it's there. But bad audio, like three day-old fish, makes its presence known by creating a stink.

As a video producer, your goal is to capture audio that is so clean and clear that it doesn't detract from the video. (This is why relying on your camera's built-in mic for anything but background audio is a mistake.) So choosing the right microphone for the job is very important. See the comparison chart at the end of this article for a side-by-side look at the features of various microphones.

Rule Number One: Audio recorded on a camcorder will almost never be as good as that captured with a standalone mic, because camcorder mics are typically ominidirectional and also can pick up the machine's operating noise. (With the move to solid-state cameras with few moving parts, this is less of an issue than it was n the days of tape-based camcorders with moving mechanical assemblies

Also worth noting: Wherever possible, choose mics that can be connected directly to your camcorder. This just makes life easier; especially when you are moving around on location. Of course, when you need to use multiple microphones and then mix the audio, such simplicity isn't really possible to achieve.

Before you start buying this equipment, you need to understand a basic principle of microphone design - namely the difference between dynamic and condenser microphones. A dynamic microphone uses a magnet, much as a loudspeaker does.

Specifically, an induction coil is attached to the microphone's diaphragm, which moves in response to the air pressure of the sounds hitting it.. These motions generate an electrical field in the induction coil, which travels into whatever device is ‘picking up the sound'.

Dynamic vs. Condenser Microphones

Typically, dynamic microphone produce enough electrical current by themselves; they do not require ‘phantom power' (external power) to amplify their signals for reproduction/recording.

In contrast, condenser microphones do require phantom power, which can come from onboard butteries, an external power cord, or from the camcorder. This is because they are based on electrical capacitors, which need power to function. In this case, the diaphragm acts as one plate of the capacitor, with the other plate serving as a reference. As the diaphragm moves, the relationship between the plates changes the capacitance voltage. These changes produce the electrical signal that serves as the audio output.

So why are there two types of mics (actually, there are more, but these are the two you really need to know about)? Answer: Dynamic mics, while good, trade off the high fidelity of condenser mics for a rugged, weatherproof package that does not require external power. This is why most handheld mics are dynamic and most examples of theother forms are condenser.

Onto the actual equipment: A well-equipped video producer has a stable of microphones at their disposal.

Handheld vs. Lavalier vs. Boom Microphones

The most important is the trusty handheld cardioid microphone. These are used on camera for interviews, and off-camera for on-site voiceovers. They can be deployed as handhelds, or mounted on noise-dampening brackets and stands. The Shure SM58 is an excellent example of a reliable, rugged cardioid dynamic handheld mic.

Cardioid microphones are unidirectional; that is, they pick up audio clearly right in front of the mic, while suppressing audio from all other directions. This is why cardioid microphones are so useful for interviews and voiceovers. The best handhelds are also designed to minimize ‘handling' noise (from being held), and use windscreens to prevent whooshing sounds on the recording.

You can also purchase omnidirectional handhelds for picking up background audio. However, because they pick up sound from all directions, they aren't often used for interviews/voiceovers.

For those who do not want to use handheld microphones, tiny clip-on ‘lavalier' condenser mics such as the Sony ECM-44B are an option. These are well suited for interviews and voiceovers. However, lavaliers are more prone to handling noise, as well as sound picked up by the rustling of clothes.

Lavaliers and handhelds can be used in both wired and wireless configurations. Wireless setups can be very convenient - as long as there are enough open channels where you are shooting to ensure interference-free transmission and reception. So play it safe: Always be prepared to shoot using either wireless or wired.

Boundary condenser microphones such as the Astatic 901R are flat units that can be mounted on tabletops. They use the surface they are on to reflect audio into the mic's pickup. Properly placed, boundary mics can be useful for gathering audio at meetings.

A fourth sound-capturing option is to use a suspended ‘boom' condenser microphone over the head of the guest, out of camera view. Typically, you'll use a shotgun mic, so named because they are directional and must be pointed directly at the sound source.

In either configuration, boom/shotgun mics like the Rode NTG-3 are highly unidirectional units. This is why they usually require a separate operator to point the unit and listen in real-time, to ensure that the audio pickup is optimized. In outdoor settings, such mics are encased in large wind-reducing shells known as ‘blimps'.

Note: Although they can double as handhelds for close-in work, shotguns are best used for distant pickups. In audio, like carpentry, you should always use the right tool for the job.

When selecting microphones, you need to consider their frequency response (the wider the better), the quality of audio they deliver (tested by recording onto a common platform, and then playing back through a single set of speakers/headsets for comparison's sake), and how well they stand up to handling noise, moving air, and ‘popping' by the talent/guests. Amazon.com and B&H (www.bhphotovideo.com) are excellent resources for consumer reviews of how individual mics stack up in these various categories.

Although it is possible to buy screens to reduce plosives - and indeed many recording studios do this for their top-end mics - smart producers select microphones that resist this problem to begin with. They also ensure that they listen to the mics' outputs using equipment they are familiar with - including TVs - to ensure that the sound being captured is what they want.

That's a basic look at the range of microphones available. Which one you choose depends on the job. A handheld cardioid does a good job for on-camera interviews, while a shotgun is great for covering speakers in the midst of crowds. An omnidirectional mic is great for recording background sound.

Worth noting: It never hurts to have a warhorse handheld microphone in your stable, like the nearly indestructible Electro-Voice 635A. Although rated as an omnidirectional microphone, the 635A works reliably for voiceovers and standup work, and is legendary for taking abuse in the field.

Take the time to assemble a stable of microphones beforehand, and you will experience far less hassle on set or location later on. The last thing you want to be doing is using the wrong mic for the job. Do this, and you could end up with audio that not only sounds ‘off', but is so bad that you have to redo the shoot. This is expensive in terms of money and time, and not as cost-effective as having the right mics to begin with.

But wait: There are still a few more thing you need to know. For instance, higher-end camcorders use three-pin XLR connecters, whereas prosumer/consumer cams use miniplugs. Rule of thumb: XLR connecters and cables do a better job of resisting noise than consumer mini-plug cords to. If possible, choose mics with XLR connectors. And in those cases where you have to bridge XLR and mini-plugs, get a BeachTek audio adaptor (www.beachtek.com) to bridge between the two.

Some camcorders have ‘intelligent' hot shoe connectors, which allow you to connect omnidirectional microphones directly into the camcorder for internal control. Most professional producers, though, will use higher-end gear that's not powered by the camcorder.

You should also consider whether you want to use wireless mics connected to a portable mixer for optimal audio intake. If you are running multiple microphones, you'll have to run them through a mixer, which allows the operator to manage a balanced output level. As for wireless: What you gain in convenience, you may lose in interference noise and audio dropoffs.

What about Mic In versus Line In: Which should you use and why? Here's another rule of thumb: Unpowered dynamics mics with their lower power output go into Mic In; amplified condenser mics and outputs from amplifier/BeachTek units go into Line In.

Okay, now before you throw up your hands in confusion, take a breath and consider what you have covered:

• You know the difference between dynamic and condenser mics 
• You know the variety of mics you can get - omni or cardioid/uni - and why they exist 
• You also know about connecter types and why they matter; wireless vs. wires, and different input channels.

In short, you now have a basic grasp of audio recording for video; anything else you can get from the people who sell your equipment, knowledgeable associates/mentors, and the Web. (Here's an excellent link:http://bit.ly/v0CljF)

The best news: You will not try to do interviews using the built-in mic on a consumer camcorder. This knowledge alone is priceless!