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Tuesday, June 21, 2011

Dual-System Sound

How to overcome the shortcomings of a DSLR’s internal microphone for professional-level video

The Zoom H4n and Roland R-44 are high-quality audio recorders that are ideal companions for HD DSLRs.

The new generation of HD-capable DSLRs offers a number of creative options, but falls down in one critical area. The problem is that the microphone element can only pick up sound at the camera. If the talent is speaking several feet away, background sounds can render the track almost unusable, not to mention the sound of the zoom lens and general camera-handling noise. Even using a separate microphone isn't without its own problem of extra cables, although that offers a better result than can be obtained from a built-in mic. Additionally, consider a low-cost windshield to dramatically reduce wind and handling noise while working outdoors.

A far better solution is to let the DSLR secure high-resolution images and use a separate digital recorder to capture the sound. And, if the project warrants the expense, you also may want to consider using a small mixing console to both blend the sounds from several microphones, as well as pan and adjust treble/bass frequencies to tailor the sound. The choice of mixer depends on your budget, but several models accommodate up to four mono microphones (or a pair of stereo devices), whose outputs can be blended into a stereo signal to be recorded on an outboard recorder.

The sound recorder used in such a double-system configuration doesn't need to be fancy. There are several species of relatively inexpensive two-channel recorders that can output standard file formats for use in your choice of video-editing system. Key technical parameters to look for are sample frequency, the digitization rate (expressed in kHz or samples per second) to match your editing system's and bit depth (generally, 16- or 24-bit; the former is normally used). Operational factors include fixed or removable storage media—the former eliminates the need for USB/Firewire connections, and the latter enables double-duty with existing SD and CF media, for example—and various file formats, including AIFF for Mac users to WAV for Windows-based PCs. Avoid using data-compressed formats such as AAC and MP3 since they can compromise audio quality and produce artifacts during subsequent AV encoding stages.

Audio Capture Option
Recorder choices include the Zoom H4n Handy Recorder (available for under $300), the Sony PCM-D1 two-channel portable audio recorder (around $1,500) and the Sound Devices 702 digital recorder (close to $1,800). Other cost-competitive brands include Marantz, Roland and Tascam. Several of these models also feature built-in microphones that, in a pinch, can be used close to the talent—maybe below the frame line, placed on a table or even in a shirt pocket if the unit is small enough—to pick up a better signal than what's available at the camera location.

If you opt to use a shotgun microphone connected to an outboard recorder, best results can be gained by adding a boom and windscreen, and aiming the mic as close as possible to the talent's mouth from just out of the frame line, or in the general direction of the action if it's a crowd scene, again, making sure the boom-mounted mic is out of shot. Look for models from such vendors as AKG, Audio-Technica, Azden, beyerdynamic, Fostex, MXL, RØDE (its VideoMic Pro can be used either on the camera or handheld), Sennheiser and Sony. Rycote offers a range of windshields and shock mounts.

For indoor work, a clip-on lavalier microphone is particularly useful for talking-head videos; add a low-cost wireless transmitter/receiver if you need extra mobility. Alternatively, a stand-mounted microphone can be used to good effect if you're in a situation where such devices wouldn't look too much out of place. And if you're using a small mixer, an additional pair of microphones can be used to secure more of a natural ambience for the soundtrack; more microphones can cover other members of an ensemble, for example.


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