Audio and Visual Perception

When you look into a camera from across the room, and you are using a wide angled lens and things are well lit, you can see the whole room. Simple right? Well the same philosophy doesnt apply to sound. Anyone who has used a camera with it's built in mic knows that. If you are interviewing someone up close, that built in mic can be adequate if it's a quality mic. But as soon as you step back, the quality of the audio goes down dramatically. It gets "roomy" or "boxy", and often times the background noise level (Noise Floor) goes up, making the already poor sounding dialogue harder to hear. How do we avoid this?

You've seen plenty of times the guy with the long boom pole and the headphones. Thats usually the best answer. Simple right? Get the mic close to the source of sound, ie: get the mic close to the actor's mouth. This makes sense right? Thats why a singer sings into a microphone, and not just in the general area of the mic. The closer you get the mic to the source of the desired sound, the better that sound quality will be because you then can turn down the mics input level (Gain), which will reduce the Noise Floor.

For Filming purposes we usually use what's called a shotgun mic on a boom pole. I wont get into the technical jargon on that, but do know that it is a different kind of mic than the kind you would use to sing into. It is a specialized microphone, and can generally serve for only this purpose, though a creative sound guy could use it for other reasons as well. But generally speaking, a shotgun mic is supposed to be able to pick up audio in a straight line from the tip onwards, with it's pickup range gradually getting wider and less sensitive. So the closer you can get that mic to the actor's mouth without being in the shot, the better.

Fortunately most of the time shots are pretty narrow, so you can get in pretty close. Shotgun mics provide the best sound, so you want to use them whenever you can. But sometimes the shot is wide, and you can't get the mic in close enough to pick up a good signal. What do you do then? Well, there are two options:

1: Use lavs. Lavs are tiny mics placed on the actor. Some are wired and go directly to the sound mixer, some are wireless and have bulky transmitter packs that too need to be hidden on the actor. Lavs are very expensive, and dont always sound as good, but are a good backup system in case the boom cant get a good signal.

2: ADR. Automatic Dialogue Replacement (though far from being automatic) is a last resort for a number of reasons. It costs money to do it (and not a lot of facilities do ADR, or have experience doing it), actors dont like doing it (assuming they have any experience doing it), you lose the performance in the actors voice more times than not, and you have to go in and re create that scene a lot of times from a sonic perspective, which is tedious and expensive.

So as always, it comes down to making sure you do things right the first time around, instead of wasting time and money for everyone involved. And again, the best way to get good production audio is to hire a professional staff and ensure that not only are conditions ideal for sound recording, but the proper equipment is available.