Sound Advice: Working the Room

Hal Robertson
February 2005

Virtually every video includes some kind of dialog. Unless you're shooting outdoors, that dialog will take place in some sort of room and it's rare to find a room that's an acoustic dream. Tall ceilings, hardwood floors and even furnishings contribute to the sonic signature of each space -- often in a negative way. Short of hiring a construction crew or canceling the shoot, what can you do? With a few accessories and some ingenuity, you can minimize the influence of room acoustics on your next shoot. Let's investigate a few common scenarios and some tips and tricks to improve the quality of your recorded dialog.

As you may recall from your high school science classes, the sound we hear is actually air moving outward from the source in waves, like ripples in a pond. Like those ripples, the sound radiates from its source and fills the room. Even though the human voice is somewhat directional, a portion of the sound works its way around the sides and even the back of the subject. When the waves of sound run into a boundary such as a wall, floor or ceiling, they bounce back. The amount of bounce depends on the hardness of the surface and the pitch of the sound. Your microphone picks up the original sound, but it also picks up the bounced sound to some degree. This creates the hollow effect you've probably heard from time to time in your videos. In very reflective rooms, you may even hear individual echoes. If you're shooting a sports video in a racquetball court, the reflections actually add to the impact of the sound, but for a more intimate subject, the echoes can be very distracting.

In addition to basic reflections, each acoustic space has something called room modes. Room modes are a function of the length, width and height of the space and cause certain frequencies to resonate more than others. Using a little geometry and algebra we can even calculate which frequencies will be the biggest offenders. You don't have to go to all that trouble; it's enough to know there is a reason why every room sounds different.

Suck-outs are another acoustical phenomenon to be aware of. This term refers to places in every room where certain frequencies are actually absorbed more than others. It takes some time to learn what to listen for, but a few extra moments in a room could help identify a location for your shoot that sounds better than another.

Before we get into the subject of acoustic treatment, let's see how microphone choice can reduce the effects of nasty room acoustics. Consider a typical interview with the subject seated midway between the camera and the background. In an effort to minimize stress on the talent, you've chosen a shotgun microphone suspended in front and above her head, just out of frame. Although this microphone is very directional, it's still subject to the sound reflections we mentioned earlier. In a lively room, you will pick up the sound of the space in addition to the dialog. Using headphones, listen to the subject as she answers some sample questions. Try different microphone angles and positions, choosing the one that offers maximum voice and minimum room. While the overhead position is usually preferred, don't rule out a lower position looking up. This simple change may be all you need to get the sound that you want.

As an alternative, consider switching to a lapel microphone. Although it requires a bit more fuss with the talent and her clothing, a lapel microphone offers two distinct advantages in a reverberant room. First, the microphone is naturally closer to her mouth and, although it will appear in frame, you can move it even closer if necessary. Second, the subject's body blocks half of the influence of the room. Highly absorbent clothing like a sweater can even soak up some of the offending acoustics. Don't bet the farm on this technique, but it may just be the ticket in certain situations.

• Digg This!
• del.icio.us
• Technorati
• StumbleUpon
• Reddit