Learn how to tackle the challenge of recording audio in a large room.
It's inevitable. If it hasn't happened already, you'll eventually shoot video in an auditorium. Aside from potential problems with lighting and available electricity, how will you record the sound? Authorities will probably confine you to some horrible cubbyhole at the rear of the auditorium with little or no chance of using your camera's built-in microphone. With a little planning (and a bag full of audio goodies), you can take control of the situation and turn this potential dilemma into a great recording.
You Want Me to Shoot Where?
Whether the request comes from your wife, a teacher or a paying client, you'll end up shooting video in some pretty bizarre locations, each with its own set of quirks. Without a physics lesson, just understand that each environment transmits sound in different ways that will help or hinder your efforts. Rooms with tall ceilings sound different than rooms with low ceilings. Rectangular rooms sound different than octagonal rooms, and so on. The length, width, height and shape of each auditorium factor into its sound. And building materials, furnishings and carpeting (or lack of carpeting) also play into the equation. In fact, every auditorium has a unique sonic signature that defines how it sounds when recorded.
Of course, I'm using the term "auditorium" generically. You may be shooting in a performing arts center (very good) or a gymnasium (very bad). Recognizing some of these differences will help you minimize the detrimental effects of auditorium acoustics.
Connect With the Source
Whenever possible, the best way to get great video sound is to take it directly from the house sound system. While it's not an option in every situation, this technique is an excellent way to virtually eliminate the acoustic effects of the room. Although this method requires some preparation, you'll find the results can be extraordinary.
First, you'll want to visit the venue before the performance date. (You were going to scout the location, right?) Make a note of possible camcorder locations and their proximity to the house sound system. Positioning yourself near the sound system will make hookup easier, but may also result in a poor camera angle. You'll have to decide on an acceptable tradeoff.
Next, make friends with the sound system engineer. You need his cooperation to make the audio connection, and he may have some advice based on previous video events. Of course, you also need permission to plug into the sound system; don't just assume this is possible. There may be a technical or administrative reason that prevents your connection to the sound equipment.
Whatever the situation, make sure you have all the hardware necessary to connect to the sound system (see the wiring diagram in Figure 1). It's impolite to ask the house engineer for equipment you should have brought. This may include connectors, adapters, impedance-matching devices, direct boxes and any number of other audio goodies. Remember that the output from most sound systems is at line level, not microphone level, and you'll need a way to compensate for the difference. If you shoot with a consumer or prosumer camera, you'll also need adapters to plug into the 1/8-inch microphone jack on your video camera. And don't forget a good pair of headphones to monitor the audio.
If there is no way to connect to the house sound system, a carefully placed microphone could be the solution. Although this is not ideal, the outcome will be acceptable if done properly. Microphone selection, based on the size and shape of the room, is important. You need a mike that will accurately represent the sound without coloring it too much. Typically, a stand-mounted directional microphone placed in front of the sound system speakers will do the trick. If more audience reaction is preferred, substitute an omnidirectional microphone. Distance between the speaker and the microphone determines the balance of sound. If the speakers are mounted high on a wall or suspended from the ceiling, try a shotgun microphone as the last line of defense.
Let's Get Serious
What if you want full control of all the sound on your video? You can mike the performers with your own gear and mix the performance yourself. Unfortunately, full control requires a great deal more equipment, a much more complex setup and perhaps another pair of hands.
Let's pretend little Jimmy has the lead role in his first play. The school auditorium doubles as the gymnasium and the sound system does little more than cover ball games and assemblies. You graciously offer the use of your wireless microphones and other video equipment to get a proper recording of the play and mark little Jimmy's thespian premiere. The drama instructor thanks you and begins to outline what you'll need: four wireless mikes for the main characters, two or three extra microphones to pick up additional dialog, one mike for off-stage sound effects and an additional mike for the orchestra!
After you regain consciousness, you realize this requires a mixer to combine the 10 microphones, cables for every mike and/or receiver, five or six mike stands and an audio operator to keep things under control. A simple school play has turned into a monster.
A simpler example is a wedding shoot, with a microphone for the room and a wireless mike on the groom or minister. Regardless of the house sound, you can blend your two mikes in the field with a mixer, or record each on its own audio channel and mix them during editing.
The Natural Approach
If you're shooting a band, orchestra or choir concert, the best method for sound pickup may be to mike the performance itself, rather than rely on the sound system. In the November, 2001 issue of Videomaker, we discussed several ways to record a program in stereo. Without rehashing the entire article, here's the general idea. Mount two identical mikes atop a tall (10- to 15-foot) microphone stand. Center the stand in front of the performing group, behind the conductor. The shape and size of the room, along with the size of the group will determine the distance between the microphones and the performance area. There is no magic distance here; let your ears be your guide.
Again, microphone selection is important. Directional mikes emphasize the sound in front of them while non-directional mikes pick up sound equally in all directions. Depending on the location, either can work to your benefit. You can position the directional mikes farther back in the auditorium to capture a broader soundscape. You may have to place non-directional microphones closer to the source, but with no additional equipment, they will equally pick up applause and audience reaction.
Final Sound Byte
As you can see from these examples, auditorium audio has many obstacles. This is a unique discipline that requires extra equipment, patience and the ability to think on your feet. Once mastered, however, your video recordings will posses a sound quality like no other. Even if you don't make an extra dime for your trouble, you'll have the satisfaction of knowing you did it the right way.