Producing Great Sound for Digital Video
By Jay Rose
When Friedrich von Schelling wrote that, he was being poetic. The scientific truth is if there were such a thing as frozen music, it would be pressure. Usually air pressure; but it can also be water pressure, wood pressure, or pressure in anything else that conducts sound. Just pressure. Not the kind of pressure you feel when deadlines approach, but pressure that compresses molecules together. These molecules can be of almost anything: sound usually travels in air, but the same principles hold when it's traveling in water or across a solid.
If the pressure keeps changing repeatedly within certain speed ranges, you've got sound. Something -- a drum skin, human vocal cords, the cone of a loudspeaker, or anything else that makes noise -- starts vibrating back and forth. As its surface moves towards us, it squeezes air molecules together. As it moves away from us, it creates a very slight vacuum that pulls the molecules apart.
If we could freeze sound and see the individual molecules, they'd look like Figure 1.
Figure 1: If we could see sound, it would look like this. Air molecules are squeezed together and pulled apart by the vibrations of the tuning fork.
Think of Figure 1 as a snapshot of a single moment in the life of a sound. Air molecules are represented as tiny black dots . . . and as we enlarge sections of the picture, we can see individual ones.
Air molecules, like everything else in the physical universe, take time to move from one place to another. So even while the pressure is spreading outward, the tuning fork -- which is vibrating back and forth -- may start moving back in the other direction. The air molecules next to the fork rush back in to fill the space where it was, pulling them a little further apart than normal. This very slight vacuum -- engineers call it rarefaction -- pulls on the next layer of molecules a little farther from the tuning fork, spacing them apart. And the process repeats to successive layers.
But these sequences can be more effective if you're also recording natural sounds, dialog, or the characters singing. This kind of shot requires preproduction planning, and you'll need an experienced production sound recordist to help you sort out the options:
ADR is expensive, exacting, annoys the actors, and seldom gives you a wonderful soundtrack. It should only be considered as a last resort in video production; often, compromising slightly on the choice of location will yield a better overall project. If you must use ADR, it helps to plan ahead:
The actual techniques for ADR are discussed in Chapter 8.
Figure 1: If a boom section is extended all the way (top), it won't be as strong as if it overlaps (bottom).
The clutch that locks the sections of a boom when they're extended can wear out and become difficult to use. A layer of plumber's Teflon tape around the threads usually fixes things.
Sometimes sections of a collapsed fiber boom can get stuck together, particularly if it was moist when stored. Gentle heating can usually get things moving again.
Figure 2: It's easier to hold the boom with your arms straight up . . .
Figure 3: . . . not out to the sides.
It may be tempting to hold the boom like a flagpole (Figure 4), but this gives you less control over how the mic is aimed. Since the boom itself will be at an angle, it's likely that it'll cross into a corner of the shot.
Figure 4: Don't hold the boom like a flagpole.
If you can, hold the pole a foot or so in toward the middle rather than at the very end. This way part of the boom can act as a counterweight, and you won't be stressing your wrists as much.
Isolate the microphone end by making a small loop in the cable and securing it with a piece of tape. The loop should be just big enough to keep from slipping into the boom.
Then, loop the mic cable around your finger where you're holding the boom, and pull slightly to keep the cable taut.
If you're using a boom where the cable has to run outside, tape the microphone end of the cable tightly to the boom. Wrap the cable around the boom a few times on its way down, and grab the cable along with the boom.
As the boom is swung around, a loose XLR connector may rattle and create electrical or mechanical noise. To be safe, secure the connector to the mic by wrapping it with tape.
If you're using a desktop NLE, follow the steps below. If you've got a different kind of system, the procedure will be only slightly different. Read along through these instructions, and we'll cover the differences later.
Start tapping the marking button very lightly on each count. When you get to each "one," tap hard enough to actually make a mark. Depending on your system, you might then have to switch to a different button to mark the next "one" without erasing the first.
Figure 9: Tap hard enough to make a mark each time you count the number 1.
Copy the clip to a timeline, and you're ready to edit. If you want to shorten the piece, cut out the space between two marks and butt the pieces together. In Figure 10, we cut from Marker 2 to Marker 4, pulling out about three seconds. (Because of the way chords flow in most music, it usually sounds better to cut from an even number to another even one, or from an odd number to another odd one.) If we wanted to extend the music, we could have taken that stretch between Marker 2 and Marker 4 and laid it into the timeline twice.
Figure 10: Shortening a cue by cutting from one numbered mark to another
This is a very short edit -- there's only about three seconds between the markers -- but the technique works for edits of any length. If you need to edit longer stretches of music, make the marks farther apart. . . say, every fourth "one".
Figure 11: An edit can be before or after a marker, but the markers still have to line up.
In Figure 11, we built the edit on two tracks and added a quick fade up to make the entrance of the horn melody smoother. But you can do a similar edit on a single track, making a butt cut from one marker to the other, and then rolling the edit point forward to pick up the melody. The important thing is that, no matter where you make the edit, you still preserve that constant heartbeat -- the length of time from one downbeat to the next has to stay the same.