The trick to good video: good audio. Ever wonder what kind of mic they use to pick up the guys talking in the middle of a battle scene where entire star systems are exploding left and right? Answer: They don’t even try to get good audio. They get what they can, then in post-production, replace the dialog in the studio. (Just to confuse life even more than it already is, this is called “looping,” although it has nothing to do with looping as in samples that sustain, or looping like groove boxes.)
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But when you’re shooting your rock band with a camcorder, or making some bucks on the side doing sound for an industrial video, you don’t have that luxury. And the mic in your camcorder probably sounds like it came from K-Mart. So what’s the ticket to good audio?

The answer lies in a technique from the distant past: “Flying in” audio recorded separately (also called “free sync” or “wild” sync). Basically, you record the audio on something small and convenient, like the new generation of portable recorders that record to solid-state memory, professional Minidisc recorders, and so on. (See page 60 for recorder reviews.) Virtually all of these let you transfer audio to the computer where you’ll be editing your video. The person doing the talking can usually wear a lapel mic, and keep the recorder in a pocket or attached to a belt. This beats trailing a bunch of cables back to the camcorder mic input (although the latter adds excitement when someone trips over it and rips the connector out of the camcorder).

During the editing process, you then line up the well-recorded audio with the crapistic audio from your camcorder mic, and once you have them in perfect sync, you mute the camcorder audio (not erase, just mute) so you don’t hear it.

Sounds easy, right? Well, there can be some complications, so let’s address them.

In the days of analog, flying in parts was hellishly difficult because of the timing instability of analog devices. With digital, drift is much less of a problem but still exists. Even though your camcorder and recording device are both digital, the slightest timing discrepancy in their little crystal-controlled brains means that eventually, they’ll drift apart. Even a few milliseconds’ difference between when someone says something and when you actually hear it is noticeable.

If the audio drifts behind the video, then periodically make a cut in the audio and slide it ever-so-slightly forward in time (i.e., to the left) until their peaks match up perfectly. Make the cut at the beginning of a word, preferably one that starts with a plosive (P or B) to help mask the cut. With music, cut at a drum hit. The more cuts you make, the less you’ll have to shift each segment of audio, and the less noticeable any shift will be. But in general, you’ll probably need to do this only every minute or so.

If the audio runs ahead, then matters get slightly more complex. Look for pauses between words, make a cut at the beginning of a word, then move the file slightly to the right. However, this will leave a gap and you have different ways to deal with it:

  • If there are a lot of other sounds going on, the gap may not even be noticeable.
  • Try adding a short fadeout to the section leading into the gap.
  • Copy a portion of the sound just before the gap, then crossfade it with the section at the end of the gap to extend it (Figure 1). If this is short enough, no one will notice.

If none of these options is possible, then look for a better place to make the cut.

It may sound tedious to match up good audio with the existing audio, but in reality, it’s not hard at all — and certainly easier than having someone come in and try to loop the dialog.