Capturing Good Sound Indoors

When you shoot outdoors you run into audio problems constantly. Cars rush by on busy streets, airplanes roar overhead and annoyingly cheerful people laugh just outside your frame-and all of these noises find their way onto the audio portion of your videotape where they mar otherwise perfect takes.

Moving indoors will cure these ills so your troubles are over, correct? Ha! as we say in the business. Just remember this next phrase and you can’t go wrong. Nothing is ever easy.

Interior locations are beset with unique problems. Listen carefully: fluorescent lights buzz; air conditioners hum; poor construction in some buildings allows traffic and aircraft noise to intrude into your scenes.


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But you can work around these problems (and even fix some of them in post production) if you understand how sound works.

The Nature of Sound

Sound emanates from the source- for example, your mouth when you say “Ha!”-as a disturbance in the air. These vibrations act like waves. Your ha! floats through the air until it hits another surface, like a wall.

If the wall is steel (where do you live, Fort Knox?), most of your ha! will bounce back in your face. If the wall is padded (a possibility if you go around yelling ha! all the time) then it will absorb much of the sound.

When I was in college, I performed in several choral groups. A strange admission, I admit, but there is a point. Whenever we traveled to a concert and went to practice in the auditorium, church or concert hall (where we had never performed before), several members of the group would click their fingers or clap their hands. This ceremony seemed very hip at the time, although I didn’t know why they were doing it.

After several repetitions, someone would declare the space “live” or “dead.” I now know that they were checking to see if the room would reflect sounds in a pleasing way. If dead, the room reflected little sound. If live, it reflected a lot.

A small room sends sound to the far wall, where it bounces back in a hurry. In a large room, it takes longer for sound to rebound. The sound also hits the front wall on the return trip and bounces off of it. Back and forth, sound goes, fading and fading until it runs out of energy. The sound of sound bouncing back and forth is reverb. The fading process is decay.

The human brain is a very clever organ. Using sound information, the brain can tell if you’re standing in a cavernous space or hanging down a well. It determines this by the way sound reflects, reverberates and decays.

The Studio Dilemma

So your job, when shooting indoors, is to eliminate all traces of reverb, right?

Ha, ha, ha, ha. No, indeed. You want this information. The trick is to make the reverb match the scene that the audience sees. If you shoot a close-up of a guiter player rehearsing in a small practice room, then the audience expects the music to sound as though played in a small practice room.
What if the practice room is not really a practice room, but a set constructed in a large studio space? The hollow audio that results will prove as incongruous as a stiff breeze tossing sheet music around the guitar player’s feet. These distractions are not what the audience expects to see or hear. It’s up to you to match the audio to the scene.

What’s happening to the sound in the studio?

The talent will strums the guitar chords, which travel up to the ceiling and to the back wall before bouncing back. Then they come back and bounce off the floor and the wall.

So you need to make the sound bounce like it would in a real practice room.

Start by putting carpet on the floor. This will absorb the sound so that it does not travel back to the ceiling for a second time. This “practice room” only has a back wall, made of flats-stretched canvas over frames painted to look real. Add more flats to create a corner. Hang sound barriers on that side of the “practice room” from which you’re shooting. This will keep the sound from reaching the back wall of the studio. The barriers can be blankets, foam core sheets or more flats.

Again, you want some reverb, but only enough to suggest that normally found in a small practice room.

All the World’s a Studio

Moving out of the studio and back into the real world, you find yourself shooting in a real practice room.

Here you may face the opposite problem. A very small room with smooth, parallel walls will create sound that bounces quickly. This means a harsh, unpleasant effect, especially on sharp sounds such as footsteps. Stop these sounds before they go too far by hanging a thick blanket on the wall across from your sound source.

The key to good audio: training your ears to hear everything in a location. Before the talent arrives and you set up the equipment, listen. Better turn off that air conditioner before you roll. Otherwise, youll have to put up with a low frequency hum. Of course, if you do turn the cool air off, your talent may suffer excessive sweat or heat exhaustion under those hot lights. You may need to cycle the AC on and off between takes.

Are you pumping music into the room? This is dangerous, especially when the music is so quiet it lingers at the edge of perception. You may not notice it until you get into editing (where is that Mantovani coming from?) when theres nothing you can do about it.

So listen. Is someone playing a radio in the next room? Can you hear it? Your microphone may also pick it up.

Fluorescent lights not only emit an unflattering greenish light, they also make noise. These fixtures turn themselves on and off thousands of times a minute. This frenzied activity creates a buzz that some microphones can pick up. Again, listen. You may have to turn these lights off and use a light kit.
If your location boasts a window overlooking a busy street, you must deal with traffic noise. A couple of heavy blankets may deaden this unwanted ambience. However, if the windows in the shot and the viewers will see the big city outside, you may want to leave some traffic noise.

The Sound of Widgets

Say you’re shooting a documentary on the workings of ABC factory. You need an interview with the foreman, but the only time he can talk to you is while he’s on the factory floor.

Down there, huge machinery clatters away. Doomed? Not necessarily Audiences are more forgiving of such noise when they can see what’s making it. Find the least noisy part of the room; then compose your shot so the machinery is behind the foreman.

Get your microphone as close to the foreman’s mouth as possible; use a directional microphone if you have one. This will minimize the ambient sound, giving you the best audio you can get under the circumstances.

One more problem you may encounter: the buzz from electrical extension cords or other power cords. This can happen when you run an audio cable parallel and close to a power cord. You can avoid this by separating the cables and only crossing audio and power cables at a 90- degree angle.

The External Microphone

Of course you won’t experience any of these problems without a microphone. Nor will you experience any audio on your tape.

Microphones grace the top of most camcorders. These camcorder mikes work well for documentary-style shooting, where you want to hear the sound created by the subject in the frame. But you also know that as you move away from that subject, the sound becomes less distinct, more hollow and not as loud. That’s because the closer the mike is to the subject, the better the audio. So sometimes you need an external mike.

Lavalieres (lavs). These are small mikes used by news anchors, talk show guests and the like. These mikes clip to the subject’s tie, lapel or dress. The best position: a few inches down from the person’s chin. With the pickup- area of the mike pointing at the subject’s mouth, the result is fairly decent audio.

The advantages of using a lavaliere

1) Each person in the shot can wear a separate mike. So if one person talks loudly while another mumbles, the audio engineer can adjust each person’s audio individually.

2) Lavs move with the subject and stay in the same relative position to the sound source (something a boom operator has to be trained to do).

3) Lavs are small enough to hide under ties or inside blouses for shots where you don’t want the mike to show.

Some of the disadvantages:

1) Most lavs are hard-wired to the video recorder or mixer. If you frame your talent in a wide shot you might see the cable running out from inside the legs of his pants.

2) Lavs don’t always sound that great. Hide a lav under clothing, and the material may scrape against it, causing a rustling noise.

3) Each person in the shot needs a lav.

Stick mikes. The microphones come in many forms, from the all-purpose, handheld mike used by news reporters for standups, to the shotgun mikes used for sporting events. The stick mike is often a prop; the reporter jabs the mike toward the crooked politician after asking a particularly scathing question; the singer croons into the mike with dramatic finesse.

In standups and interviews, the talent can point the pickup area of the mike back and forth at the appropriate source (themselves or the interview subject).

Warning: such moves can backfire when performed by inexperienced or nervous talent.

In these cases, the mike always points at the talent when the interview subject is speaking, and at the interview subject when the talent is speaking-in other words, completely backwards. Amusing but annoying.

The advantage of a stick over a lav: the ability to cover several people at once. More rugged than lavs, stick mikes suffer physical abuse better. Another plus: you can attach your station logo to a stick mike for a plug whenever the mike appears on camera. There are disadvantages as well, First, stick mikes are bulkier than lavs and therefore difficult to hide. Second, nervous handlers can introduce noise when they move their fingers when holding the mike.

Boom mikes. Everyone’s seen a boom mike. This is a stick mike attached to a long pole. The operator stays out of camera range (either just above or below the edge of the frame) and points the mike at the subject(s). With a good mike, this is an excellent way to capture audio for dramatic shows. The danger of the mike slipping into the frame is always present, however; the boom operator usually can’t see a monitor. Many a good take has been lost due to wayward boom mikes.

Wireless mikes. These can look like sticks or lavs. They transmit the audio from the source to a receiver that feeds the audio into the deck. Wireless mikes are great when you want to see the talent from head to toe; or when the talent is so far from the camera that stringing cable would not be feasible-way up there in that hot air balloon, for example. Wireless mikes are also handy for speakers in large lecture halls who like to move around a
lot; an audio cable could slow them down or even get wrapped around their feet if they make any sharp turns.

Radio interference sometimes plagues wireless mikes, especially around two-way radios, cellular phones or power transformers. To avoid interference, keep the transmitter and receiver in a line-of-sight configuration. Also, if you use more than one wireless at a time, make sure the systems operate on different frequencies, or the systems will interfere with each other.

Audio Post Production

But what if you put together great equipment and knowledgeable personnel, and your indoor audio still has problems? This happens on feature films all the time. Obviously, these productions boast the best sound gear and engineers money can buy. And yet filmmakers must occasionally fix it in post-that’s post production. If you have audio you don’t like, simply get rid of it and start over.

It can happen like this. You shoot a dramatic scene in an office. After a wide shot of an interchange between two actors, you move in for close-ups of the same action. While you are moving the camera, the air conditioning kicks on. No one notices it. But later, in the editing process, there’s an obvious change in ambient noise from one shot to the next. Viewers, trained to suspend disbelief when watching dramatic productions, will accept a lot. But they’re also spoiled by the high production values of TV shows and films. If your audio changes from one scene to the next, you may lose their trust (and then their interest).

Must you go back to the location and reshoot? In this simple setup, that might be the least time-consuming method. But what if your location is the president’s office that took weeks to get permission to use in the first place? What if the office is on the twenty-fifth floor, reachable only by rope ladder?

To “fix” the audio, you’ll probably have to replace the audio for the entire scene. Try to replace just the shots where the air conditioner is running and you open another can of worms: matching the audio from the scenes you didn’t replace. It’s probably faster to do the whole scene.

First, you need an audio booth where the actors can voice their lines for the replacement audio. This space should be as “dead” as you can make it, free from any extraneous noise. Put packing blankets or old sleeping bags on the walls to help knock out any echo. Or buy foam products from a professional vendor. Markertek of New York City, Illbruck of Minneapolis, Acoustical Solutions of Richmond, California and National Foam of Woodland Hills, California, all produce acoustic foam sheets.

Some manufacturers, like WhisperRoom of Columbia, Maryland, even make small, modular voice-over booths that turn any room into a vocal studio.
Your actors must be able to see a monitor. As the scene plays (or better yet, as each shot that makes up the scene plays), the actors say the lines in the same way they said them on location. You might also play the existing audio for the actor over headphones so they can hear the exact inflection they gave the line on the given take. As the actor reads the line, edit this new audio onto the scene. Do this as many times as it takes to be believable. A bad lip-sync can cause your audience to react in an unpredictable and unfortunate way. Your Kung Fu is no good. (Lips continue to move.) Ha!

Once the new lines are edited onto the scene, you’ll have good, clean audio. Unfortunately, it no longer sounds remotely natural. There is no background noise whatsoever; the words the actors speak are flat and without reverberation. That’s not what the office should sound like.

What you need now is a reverb unit. These units usually allow you to feed in your signal and alter it by adding reverb. Remember, the amount and quality of the reverb tells you where you are. A lot of reverb, and the audio sounds like you’re in a cave; no reverb and you’re back in the audio booth. Adjust the amount and “room size” of the reverb until it sounds like an office.

If you don’t have a reverb unit, try setting up a speaker in the office. Now play back your clean audio and record it onto another tape. Edit this back onto your original scene; the audio should sound correct.

But you’re still not finished. Did that office exist in a vacuum? Or should there be a hint of traffic noise from outside and the faint clatter of a typewriter down the hall?

Add these sorts of sound effects back into your mix. Be careful not to make them too loud.

Sometimes it takes a lot of effort to find and record these ambient noises and we want to show them off. Don’t.

For best results just use a hint of traffic and a dash of typewriter. Now your totally fake audio should sound totally real.

Say What?

Getting good audio is at least as difficult as getting good video, possibly more so. I know that’s not what you want to hear. You want something in the videomaking process to be easy. Sorry. Nothing is ever easy.

The other frustrating part about working your tail off to get audio absolutely right is that when you do, no one will notice it. It will sound so perfect and natural people will think it happened without any help from you.

And you thought this videomaking stuff was going to be fun. Well, that’s the crazy thing about it. It is fun. But the fun part is when your audience laughs at the right spot, or when they learn something they never knew before, or when they run out and buy the product you’re selling in your video.

And when you do it well, you’ll hear people say, “That videomaker sure makes shooting great pictures and capturing great audio look easy.”

But is it easy? You already know the answer to that.


Videomaker contributing editor William Ronat owns a video production company.

The Videomaker Editors are dedicated to bringing you the information you need to produce and share better video.