Avoiding Whirrs, Rattles and Hums
COW Library : Audio Engineering Tutorials : Michael Hanish : Avoiding Whirrs, Rattles and Hums
To Successfully Record Stereo Using Your Camera's Audio, Forget the On-Board Mic. Seriously, Forget It.
There are a number of compelling reasons not to use the onboard camera mic during shoots, especially for music.
First, microphones record best that which is closest to them. For a mic mounted on a camera, that means the camera's motor noises (transport, zoom, and focus), handling noise, and operator sounds.
Second, even a stereo camera mic will not record a very well defined stereo image due to its distance from the sound sources and its basic design. The mic has to hear stereo to record it, and that's not going to happen at the distances you normally shoot from.
Third, the microphones supplied with, or installed on, most cameras are general purpose: passable for some applications but not really the right tool for any.
Most cameras will have inputs that allow you to connect external mics for inputting audio signals into your camera.
So, how do you go get respectable stereo sound on a shoot?
Let's imagine a situation that calls out for stereo sound: a small jazz ensemble (piano, bass, drums, vocalist) performance, with a live audience. Let's also imagine (I'd say visualize, but we don't really have a word for audio visualization) what we'd like the audio tracks to be like: all performers heard in proper sonic balance with each other, accurately reproduced, and accurately placed in the stereo sound spread. We want the sonic point of view from a seat in the audience, except better, and with less distraction.
The results of using your onboard camera mic might be nearly adequate if you could place yourself between the audience and the performers, yet close enough to the band's PA speakers...but that would leave you in an untenable position for video.
FOUR BASIC AUDIO FORMATIONS
Assuming your video camera has the capability to accept two microphones as inputs (most do, see example at left), there are four basic formations for recording audio: coincident, spaced, near-coincident, and baffled omni pair.
The coincident and near coincident configurations both use directional microphones, angled about 120 degrees apart (55-60 degrees right and left of center), 8 to 10 feet from the group. The simple diagram below shows the set-up.
Your microphone's distance from the band is subject to experimentation, depending on how loud the band is and how high the ceiling is, among other factors. In a coincident pair, the microphone grilles touch, generally one above the other; a near coincident pair has the grilles spaced a few inches apart horizontally.
These two configurations may appear to be almost exactly the same, but the results show some striking differences. In both configurations, the stereo imaging and spread tend to be sharp, with the near-coincident configuration producing more of a sense of space.
Most important to consider is that the stereo image produced by the coincident pair tends to produce a mono compatible sonic image, while the near coincident pair does not. This is a vital factor if the product of the shoot is going to be heard in a mono venue, like standalone TV sets, rather than DVD production intended for a home theater, multi-speaker venue.
The spaced pair configuration features two identical mics mounted several feet apart: the farther apart they are, the wider the stereo image spread. Omni-directional mics are most common here, yielding a generally warmer ambience to the sound with better bass response, but a less sharp placement of sounds in the stereo image.
Mixdown to mono has strongly negative consequences due to phase cancellations of certain frequencies, making this a stereo recording technique that really needs to be heard in stereo or better.
Baffled omni recording mounts two omni-directional mics on either side of a hard or soft baffle, aimed at a slight angle out as if the mics were ears. The advantages are a sharp, wide, and accurate stereo spread and imaging, with good bass response. As with spaced pair recoding, the downside can be poor mono compatibility. It has the strong advantage of being sold ready-made from such noted companies as Neumann, Crown, and Schoepps.
All of these possibilities are just starting points for experimentation and refinement. They can all be set up and operated by a single shooter. With a just a little practice, you can capture the band performance, the stereo imaging, room ambience, and audience sound. It will be in better balance than anything short of a close mic-ed, multi-position set up. It will certainly be better than any camera mic, no matter how good, can ever hope to approach.
All four of these stereo recording techniques can easily reproduce the feeling of being in the audience at the gig.
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