This week, in honor of SALT and my class on getting better audio for your videos, I’ve reach back into the archives—way back to May 2007. This was part of a series on making better videos. I’ve updated it to include some new equipment, but the basic principles are still sound. That’s the great thing about solid fundamentals; they are timeless.
Repeat after me—I will not use my on-camera mic for anything other than general sound. I will not use my on-camera mic for interviews. I will not use my on-camera mic for short films. On-camera mics have one major drawback that simply cannot be overcome—they are too far from the sound source. I don’t care if it’s the cheap built-in mic on your DSLR or a $3,000 Schoeps, too far is too far.
Let's talk physics for a moment. There is a law in physics known as the "inverse square law." It has many different uses, but for our purposes in sound reproduction, it applies thusly: As the distance from a sound source is doubled, the acoustic energy is reduced by 75% (or 6 dB).
So, let's say you have someone speaking on camera, and that person is 8 feet away. A mic right next to their mouth may receive a signal of, say 65 dBA SPL (normal talking). As the mic moves from 3 inches away to 6 inches away, the signal level drops by 75%, or to 59 dB. When we get to 1 foot away, it's in down 75% again, or 53 dB. At 2 feet it drops by 75% again, to 47 db. By the time we get to 8 feet (where the on-camera mic is), the once strong 65 dB signal is now down to 35 dB. Now, this is all true in free space; but in a room, there are reflections which will minimize the drop. But it’s still significant.
Can an on-camera mic pick this up? Sure, but the problem is the noise floor of everything else in the room is at or above the signal level of the talent, including the sound of the tape transport in the camera! To paraphrase Alton Brown, that is not good sound.
Always Close Mic the Talent
The answer, of course, is to get the mic closer to the sound source. If you can't get the camera to within 6 inches of the talent's face (and you probably shouldn’t for other, non-sound reasons), you need a remote mic. You can use something as simple as a hand-held dynamic mic (like an SM 58) and use it like a television reporter. If you are going to do a lot of "reporter" type shots, the hands down way to go is a noise canceling mic like the EV 635 or better yet, its shock mounted cousin, the RE50. Long favorites of ENG news crews, these mics will allow the talent to stand in the middle of a football stadium and will still deliver great sound of just the talent.
If you want to be a little less obtrusive, you can use a shotgun mic (like the Audio Technica AT 8035), and either suspend it from the ceiling, a mic stand or a fish pole. A fish pole is an extendable aluminum or carbon fiber pole that is designed to be held overhead by another person, and allows the mic to be placed just out of the frame above or below the talent.
If you plan on using the shotgun on a fish pole, make sure you use a shock mount.
The purpose of a shock mount is to isolate the mic from the inevitable handling noises that a fish pole will cause. The shotgun on a fish pole gives you a lot of options if you have a second person to hold it. That person had better have strong arms though. I really like this option because the sound quality is generally pretty good, and it doesn't cost a fortune. I recently purchased a shotgun mic, shock mount and fish pole for our church and spent less than $300.
Of course, you can also put the shotgun mic on a mic stand. We shot more interviews than I can count when I owned my video production company, and we almost always used an AT853a on a boom stand right over the subject. We set it so it was just out of the shot, and got great audio every time. Sometimes, if the shot required it, we would position the mic below frame and point it up; this was key if we were shooting in a room with concrete floors. I still recommend the shock mount, even if you’re using a tripod, though.
Next time, we’ll look at wireless mic options, including one that might surprise you.