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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

This Article Features Photo Zoom

Singular Software DualEyes makes the process of synchronizing from multiple sources incredibly easy.
Synchronizing Sound To Picture
The are a number of ways of re-synchronizing the sound and image within a typical nonlinear editing program, first making sure that the sample frequencies and frame rates are identical—otherwise the audio may slow down or speed up against the video track. The easiest and most cost-effective way is to look for specific sync points; these can be established using a simple clapper board or even by snapping your fingers in front of the lens prior to calling "action." Then, simply slide the audio track until it matches the picture and lock them together so they can be edited as a pair during project assembly.

An alternate technique—and one favored by professional videographers and filmmakers—is to record a series of timecode pulses on both the DSLR and the audio recorder, and let the video editor automatically match these time-of-day settings used during the shot. This variant of double-system implies a more complicated—and potentially expensive—setup, since you'll need to connect the same timecode data to both devices; it also means giving up one of the recorder's available audio tracks.

The audio track recorded on the DSLR camera also can be used to help in the synchronization process as long as a key fact of science isn't overlooked. If you're using a shotgun mic close to the talent, and the camera is maybe 20 feet away (depending on the setup and lenses being used), the audio from the camera and the separate recorder won't be in perfect synchronism. Why? Simply because it takes the distant sound nearly 20 milliseconds to reach the camera compared to the outboard recorder. Such small timing differences may not be noticeable, but they should be taken into account if you end up wondering what went awry with your resync strategies.

Taking all of that into account, the sound envelopes from the camera's audio tracks seen within the editing window provide a handy graphical guide to matching audio from the recorder. Sure, the waveforms won't be totally identical, but it's surprising how useful the camera track is for rough-and-ready syncing by eye before fine-tuning against known hard-sync references.

If you have a lot of audio to synchronize to picture, you could consider a software solution—let your editing computer do the math. Two of the most popular offerings come from Singular Software—PluralEyes, for use within Final Cut Pro, Media Composer, Premiere Pro and Vegas Pro, and DualEyes, which is a stand-alone application. In essence, both utilities examine the waveform of the guide audio from the camera with the other set of audio tracks secured from the double-system recorder. Then, using a rather clever set of algorithms, the software adjusts the timelines until they match one another. Simplicity personified!

To add a professional touch to any video project, you also can record some sound effects from outdoor or indoor locations. Bird sounds, for example, or traffic sounds for a suburban setting can be blended in using the editing software's multiple audio tracks and pan/level controls. And, of course, a music track adds that finishing touch to any video offering.

Mel Lambert has been intimately involved with audiovisual production industries on both sides of the Atlantic. He's now principal of Content Creators in Los Angeles; visit the website at www.content-creators.com.


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