Before you head off to your shoot, CHECK your audio equipment to make sure mics are working, batteries fully charged, no bad cables.
Audio Basics: During The Shoot
Constantly check your audio levels to make sure the sound coming in is not too high or too low.
Depending on the complexity of your video camera, you may or may not have control over audio levels. For the simplest cameras (a hand-held handycam) with just a built in mic, you will need to have your camera close to the subject to pick up sound.
Put on your headphones and have your subject do a “testing 1,2,3” to make sure your camera’s microphone is picking up the sound.
Always wear headphones, if possible. (Some cameras, such as the DSLR's, don't have headphone jacks. Of course you can fix that by adding on a preamp audio box.)
If someone is speaking, make sure there is not a lot of background noise (traffic, wind, construction, etc). It can be distracting and make the interview unusable.
If you are on location doing an interview and a big truck drives by right in the middle of a person’s quote: A) Have the person repeat their answer or B) Get a video shot of the truck going by so that you can edit in the shot later to visually show the viewer why there’s so much noise. Or if the wind is blowing hard, get a shot of swaying trees.
Record atmosphere/background noise at each location. This may come in handy during the edit when blending the sound-mix or cutting together an interview. Basically, this just means rolling tape for a few minutes to capture some natural sounds from the area... this could be "quiet" sounds out in nature or the "chaos" of an event.
Make sure to get good close-up sounds of your subject. For example, if you're interviewing an author, get some shots and sounds of her "tap, tap, tapping" on her computer. Or if you're on a pig farm, make sure to get in close to the pigs with your microphone and capture some snorting sounds. Truly, the fun never ends in this business!
Best Microphones for Documentary Filmmaking
Is there really such a thing as the "best microphone for documentary filmmaking"? Probably not. The best microphone totally depends on any number of factors including your budget, type of shooting (interviews, news gathering, etc) and other equipment you're already using. Are you a one-man filmmaking crew or are you making a high-end documentary for the BBC or Discovery Channel?
Because you are on this page learning about the basics of audio, let's assume you're on a budget and looking for the best audio for the best price. The choices below aren't the cheapest, but they are solid microphones that can be used in multiple situations.