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Good audio is the key to any good production. Without it, documentaries tend to feel amateurish and unpolished. However, by learning what it takes to capture clean sound you can give your audio a real chance at sounding crisp, clear, and most of all - professional.
Audio plays many roles in a documentary. It can give your audience information, make them feel emotion, and give scenes a sense of reality. That's why it's so important to know as much as you can about how to capture great quality audio. In this regard, we'll be looking at the proper ways to use microphones, how to monitor sound, and lastly, how to set up and operate field mixers. With this kind of knowledge you'll be able to make sure your audio is always sounding its best.
As much as we'd like to ignore it, the reality is good audio always starts with capturing good sound. Though much of what makes audio good is simply knowing how acoustics work, the quality of your microphone still plays a big role in the quality of your captured sound. As such we're going to take a look at two of the most commonly used microphones for documentaries: the lavaliere and the shotgun.
The first microphone, the lavaliere is small in size and easily hidden. Because of this, they're best used in either interviews or wide shots. Unfortunately, they're very susceptible to clothing and wind noise so they're at their best when the subject will be indoors and stationary. The biggest trick with lavaliere microphones is to not only have the audience unaware of the mic, but your subject as well. In order to do this, you should first have your subject place the microphone cable behind their outermost layer of clothing. Then, place the excess cable along with the transmitter into their lap or pocket so it's out of the way. Lastly clip the microphone between the lapels of your subject's shirt or on the inside and top of their shirt. Doing this will hide both the mic and the wire from the audience's view and as a bonus, is easily forgotten by your talent.
The shotgun microphone, on the other hand, is a hyper directional mic that is used mainly for B-roll shooting. It's typically paired with a boom pole and may even have a blimp or wind filter in order to eliminate wind noise. These mics are incredibly handy for run and gun style shooting since they allow your subject to be mobile, but they do require some skill to operate successfully. One common mistake operators make is dropping the boom into the frame. This often happens since most boom operators want to get as close to the subject as possible in order to pick up a larger range of vocal frequencies. To avoid this, try agreeing on a suitable framing with the camera operator before the shot. Also, it's good to be careful that the boom mic doesn't cast shadows on your background and that audio cables from the microphone are wrapped securely around the pole. If not, the cables could create noise against the boom. Lastly, since operating a boom arm for a long period of time can be tiring, try to alternate between the classic overhead boom technique and an over-the shoulder boom technique. By doing this the operator can rest the boom arm on their shoulders which provides balance and rest while still being able to get higher by lifting their arms. In addition, this position also allows the operator to easily rotate the boom arm when another subject begins talking. With these techniques and some practice, the shotgun microphone can be one of the most useful pieces of audio equipment you own.
Of course using microphones properly is only half the battle. You'll also have to properly monitor the sound. For run and gun style shooting, there are typically two devices to monitor sound: a field mixer and a camera viewfinder.
Probably the best way to monitor sound is by using a field mixer. Good field mixers can give you very accurate audio levels which is helpful for determining whether or not the audio is peaking. Peaked audio is any sound that is so loud that it starts to overmodulate the sound making the audio sound muffled and distorted. Basically, this happens whenever a sound is louder than 0 decibels. For this reason, try and keep your audio levels in the -12 to -6 dB range so that you have some overhead in case your subject begins to talk louder. At the same time, audio that is below -30 decibels can be so low that speech begins to blend in with hiss and room tone. By raising these levels in post, you'll be raising unwanted noises as well - making speech hard to distinguish.
By far, the most common way of monitoring audio levels is by using a camera's viewfinder. With these monitors, you'll want to have the majority of your audio levels hitting anywhere between half to three-quarters of the way up the meter. Anything more and you risk hitting the red zone which means your audio is overmodulated and will sound less than ideal. Many external audio recorders also have a similar meter system on their displays. Even so, it is always a good idea to wear around or over-the-ear headphones at all times on a shoot. Otherwise, you'll never know when air conditioning, cable hum, or excessive noise interferes with your shoot.
With sound often becoming an afterthought for many documentarians, it's no wonder why field mixers are seldom used. However, field mixers are an important piece to any shooting kit. They allow sound operators to control multiple audio devices at once and allow you to capture a higher sound quality than is possible with a camera. As such, it's good to know what each part of a field mixer does.
Often, after each microphone has been put into the mixer, the first thing a sound operator will do is set the gain. The gain is set using the gain knob usually found at the top of the board near the input. By setting the gain to a solid level, you''ll be able to just focus on the volume slider of the mixer to fix any audio issues instead.
Most mixers will also include a pan knob for altering how much sound is being sent in each channel to the speakers. This can be useful when recording a left and right audio channel to your audio recording device or camera since both channels can be edited separately.
Next, there are usually several knobs for changing the EQ or equalization of a channel. This allows you to change how strong the high, mid, and low frequency sounds are in your mix.
One of the best perks of a mixer is the ability to phantom power microphones through an XLR cable. This means that that you can easily use a condenser style mic that needs electricity to operate, giving you more microphone choices.
Lastly, a good mixer may also have a limiter that can soften the peaks of your audio and make sure it never reaches 0 dB. This can be especially helpful when recording an audio source with a large variety of soft and loud sounds.
Any audience is far more likely to forgive badly captured video than poor audio. That's why learning how to control audio can be such a boon to a production. With the tips and techniques we've shown, you can make sure that your audio really complements your video.