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Audio: Getting To Know Your On Camera Audio

Level matching, filtering, power and signal processing are all possible without extra equipment or post processing. Of course, not every video camera includes all the features, but there are valuable options to explore here. So, if you never bothered to crack open the instruction manual (shame on you!), we'll show you what these audio tools do and how to use them on your next shoot.

If you've ever used a professional shotgun or lapel microphone, you've probably experienced the need for 48-volt phantom power. This feature, designed for broadcast and studio applications, allows the mixing console - or your camera - to supply power to condenser mics. Back in the day, phantom power came from clunky external boxes that were fine in a studio, but not exactly convenient in the field. Now, this feature is included in everything from small audio interfaces to many video cameras. Phantom power is a bit of a magic trick. Through some simple circuitry, it's possible to send power to the microphone without affecting the audio signal coming back. This allows you to use professional shotgun, handheld and even lapel microphones without worrying about batteries, opening a few more creative possibilities. Of course, if you're using dynamic microphones in the field, you won't need phantom power. You're trading flexibility and convenience for durability.

Accessing the phantom power to get audio from camera may be as easy as flipping a switch on the side of the camera, but it could be a little trickier. Camera manufacturers are hard-pressed to use valuable case real estate for switches and buttons, so they've resorted to hiding many features in setup menus. This is fine if you don't change the settings too often. Just navigate through to the camcorder audio menu, and look for Mic Power or something similar. Once it's activated, plug your mic in and test. It should work perfectly.

Consumer-grade camcorders also offer a form of lower-voltage phantom power, available at the 1/8" jack. This is for certain shoe-mounted mics and accessories. Other cameras may have an additional power jack near the mic input or supply power at the hotshoe. You won't have the ability to turn these on or off, but it's nice to know they are there. Originally designed for 35mm still camera flashes, the accessory shoe or "hot shoe" has made its way into the video world. Many cameras offer accessory shoes, but not all are powered - these are called "cold shoes". Check your owner's manual for specifics and compatible accessories. Some pro microphones offer battery power, but, if your mics are like mine, the battery is always dead when you need it most. Phantom power provides an always-available, reliable power source for your condenser microphones.

Once you have the microphone plugged in and working, you may find that the level is a bit too hot for a clean recording. This is common in loud, industrial settings, sound-effects recording and when you have your camera attached to a mixer or sound system. In these cases, you need some microphone attenuation. Mic attenuation is simply turning the input down to accommodate a wider variety of sources, but it happens before any manual volume control you may have. Make another run through the audio menu, and look for something marked Audio Level, Attenuation or Gain. It may be as simple as a Mic/Line setting or as complex as full gain settings marked in decibels or dB. If you have dB settings, they are measured in negative numbers; -60dB is more sensitive than -40dB and so on. Other cameras may offer the adjustments in an amount of attenuation. For instance, applying a 40dB reduction will better match your mic inputs to a mixer output.

If your camera offers manual level controls, you could end up using these as a form of attenuation. Rather than hidden settings, some camera models simply offer a level control that compensates for a wide range of audio levels. With this method, use the audio meters to gauge the input level, and compare what you hear with the headphones. A little experimentation will reveal a good compromise setting.

Nothing beats a good, fur-covered windscreen in a gusty breeze. But maybe you don't own one of those jewels or just don't have it with you on today's shoot. Your camera may offer an alternative. This option is called a low-cut, high-pass or wind filter. A low-cut filter does exactly that - cuts off the lower frequencies of the audio, allowing only the upper frequencies to pass through. Since wind noise usually crops up in the extreme low sound range, this can be an effective option. The low-cut filter is normally an on/off feature, with cutoff frequency fixed by the camera manufacturer. Turning this filter on often has a dramatic effect on the quality of the recorded audio, making it sound a bit thinner and sometimes lifeless. Of course, you'd rather have wimpy, clean audio than an unusable rumbling mess, so, if you need it, it's a reasonable tradeoff.