If you switch multiple-camera productions to tape as you shoot, you need to have a video mixer. There is simply no other way to mix the outputs of two or more cameras in real time. In the same way, to mix multiple audio sources live to tape, you must have an audio mixer. There are no two ways about it. By being able to mix the levels of your audio sources, you can keep the background music in the background, balance a hot audio source with one that isn’t as loud and combine a variety of audio sources at one time.
While audio mixers have all but disappeared from the computer-based edit bay, having been replaced by editing software with multi-track audio editing capabilities, nothing beats a good old audio mixer when it comes to recording sound from various sources in the field. This might mean mixing the outputs of several mikes for experts on a panel discussion, adding commentary to a sporting event as the game is played, or adding background music or sound effects. To get these different sounds onto the same audio track, and mixed so that each sound is at just the right volume, you’re going to need to use a soundboard. Let’s take a look at what a soundboard is, and what it can do for you.
Audio mixers come in two basic varieties. Active and passive. An active mixer requires either AC or DC power, a passive mixer requires no power at all. A passive mixer allows you to adjust the level of a mike from 0% to 100% (the full, unrestricted capacity of the mike itself). An active mixer has an amplifier and can actually boost a signal beyond 100%.
Audio mixers can be intimidating to new users. They are covered with sliders, buttons, dials and ports. Once you understand what they all do, you’ll find that audio mixers are really rather friendly creatures. The number of channels a board has equals the number of audio sources that the particular soundboard can accommodate. Keep in mind that stereo feeds require two channels if you’ll want to be able to mix the left and right channels of the audio to different levels. Many mixers will let you adjust the high, low and mid ranges of each channel independently. This feature will let you use the soundboard as an equalizer for every audio feed you have. Some soundboards will allow you to add effects like echo and reverb.
The type of inputs that your board can use will determine what kind of sound equipment you can use with it without having to use a bunch of adapters. Common inputs include XLR microphone inputs, 1/4-inch and RCA. Some inexpensive soundboards include 1/8-inch mini-jack inputs, but most professional mixers do not. If your mike has a plug that your mixer cannot accommodate, you’ll need to use an adapter to make the connection. Some condenser mikes require that power be supplied from the soundboard. If you have this type of mike, you’ll need to use a mixer that provides phantom power. Phantom power can be a key feature for the videographer (especially the videographer using the more-expensive condenser mikes).
If you plan to use professional-level microphones, make sure that your soundboard can accommodate XLR inputs. If you plan to connect camcorders and CD-players only, you can get by with a soundboard that only accepts 1/4-inch plugs (and using an adapter to make them 1/8-inch plugs when needed). If you want to be able to adjust the bass, treble and mid-range of each channel, make sure that you get a soundboard that offers those adjustments. While sliders are easier to adjust than dials, especially for volume, dials tend to be more compact and make a smaller overall soundboard. Meters are nice to have, but they should not be relied upon entirely. There is no better tool for recording audio than a good pair of headphones (see sidebar "The Headphone Zone").
Using a Board in the Field
The first and most obvious use of an audio mixer would be in a multiple-camera shoot that uses a number of external microphones. A good example of this might the panel discussion mentioned earlier. Perhaps you have each of the four panelists and the moderator rigged with microphones, a mike on a stand for questions from the audience, and a CD player to add music. For a shoot like this, you’d want at least seven channels, one for each of the mikes, and an extra channel to add in the background music. Using a setup like this, you could mix the audio portion of the discussion on-the-fly, with someone adjusting the level of each microphone as people speak, then bringing up the level of the music at the end of the discussion. Mixing in the field this way, can save you a lot of time in the edit bay.
Mixing in a Linear World
If you are one of the few editors still working in the linear world, editing multiple tracks of audio can be a trying undertaking. In the digital world you’d capture each sound source to the hard drive, then place each file on the timeline and adjust the levels of each clip to sweeten the mix. In the computer, the process is rather easy. But this type of sound mixing is more complicated in a linear editing scenario.
Sound mixing for linear editing often needs to happen on the fly. You plug the audio outputs of each source machine (camcorder or VCR) into its own input on the soundboard, the output of a CD player into another and a microphone, for narration, into another. The output of the soundboard is run to the record VCR. You can use the volume level adjustments to swell the volume on the background music when you want it, or to match the levels of the audio recorded alongside the video, and the audio from the narrator’s mike.
Get What You Need
Don’t take this as a recommendation to go out and get the most-expensive soundboard that you can afford. For most video applications, you’d be able to do wonders with a six channel board that can run off of batteries. This way you could use it in the field, or use it in the edit bay.
Don’t think you’ll never have a use for an audio mixing board. They are handy to have, even if you edit all of your video on the computer, and can also be used with a variety of audio equipment. If you care enough about your audio to use an external microphone, and you should care that much, you probably have a need for a soundboard too. If you stick to a small basic board, you can probably get what you need for less than $100. If you think you need quite a few channels, or fancy effects processing, you’ll probably end up spending a lot more, but then you’ll have the audio power that your video productions need.