Module 41

Updated: 07/07/2005

Using Off-Camera
Microphones

Although it may be appropriate to use handheld, lav, or RF mics for interviews, there are instances in television production when it's desirable to use an unseen microphone - generally one that's outside of the camera's field of view.

Examples would be:

• because seeing a mic wouldn't be appropriate, as in the case of a dramatic production
   
• when mic cords would restrict the movement of talent, such as in a dance number
   
• when there are too many people in the scene to use multiple personal, handheld or RF mics, such as with a choir

Because of their nondirectional nature, omnidirectional or simple cardioid-patterned microphones used at a distance of 1½ meters (five or six or feet) or more quickly start picking up extraneous sounds. Depending on the acoustics of the situation, this can also cause the audio to sound hollow and off-mic.

Consequently, only microphones with a supercardioid or narrower pattern should be used as off-camera mics.

Just as the eye sees selectively and may not notice a coat rack "growing out of" someone's head in a scene, the ears hear selectively and may not notice an annoying reverberation in a room, which, when picked up by a mic, can render speech difficult to understand.

Room Acoustics

Whenever a room has smooth, unbroken walls or uncarpeted floors, reverberation (slight echoes) can be a problem.

Moving mics closer to subjects is the simplest solution, but this is not always possible. Other solutions include using highly directional mics, adding sound absorbing materials to walls, or placing objects within a scene that will absorb or break up sound reflections.

As we previously noted, one type of highly directional mic commonly used for on-location shoots is -

The Shotgun Mic

  Because of their highly directional characteristics shotgun mics can be used out of camera range at distances of up to 10 meters (25 to 30 feet).

As with all directional mics, they have to be carefully aimed, preferably with the aid of high-quality earphones.

Shotgun mics are often mounted on -

Fishpoles

The quickest solution for picking up audio, especially in on-location shooting, is to attach a directional mic to a pole and have someone hold it just out of camera range.

As the name suggests, a fishpole consists of a pole with a mic attached to one end. The position shown here allows good audio pickup, while the camera (out of range on the left), holds a closeup of the talent.

An operator equipped with an audio headset to monitor the sound being picked up can move the microphone according to changes in camera shots and talent position. Supercardioid and hypercardioid mics mounted in a shock mount (a rubber cradle suspension device) are commonly used.
  

Microphone Booms

In the studio the simple fishpole moves into the much more sophisticated category of boom mics.

Microphone booms range from a small giraffe (basically a fishpole mounted on a tripod) to a large perambulator boom (that weighs several hundred pounds, takes two people to operate, and can extend the mic over the set from a distance of 100 meters (more than 30 feet).

The largest booms have a hydraulically controlled central platform where operators sit and watch the scene on a TV monitor while controlling such things as the

• left or right movement (swing) of the boom arm
• boom extension (reach of the arm)
• left to right panning of the attached microphone
• vertical tilt of the microphone
   

Hanging Microphones

Sometimes you can get by without a boom mic, especially if the talent is confined to a limited area. In this case a mic can be suspended over a performance area by tying it to a grid pipe or fixture just above the top of the widest camera shot. The disadvantage of this approach, of course, is that the mic can't be moved during the production.

Both boom mics and suspended microphones should be checked with the studio lights turned on to make sure they do not create shadows on backgrounds or sets.
  

Hidden Microphones

It's sometimes possible to hide microphones close to where the on-camera talent will be seated or standing. This will eliminate both the need for personal or handheld mics and the problems that mic cords can introduce.

Microphones are sometimes taped to the back of a prop or even hidden in a table decoration, such as the vase of flowers shown here.

When placing mics, keep in mind the proximity effect discussed in an earlier module. You may find during an editing session that the audio from different mics used at different distances will not "cut together" without annoying changes in quality.

Sometimes several mics must be used on a set at the same time. In this case each mic not being used at a particular moment should be turned down or switched off. This not only reduces total ambient sound, but also eliminates something called -
  

Phase Cancellation

Phase cancellation, which results in low-level and hollow-sounding audio, occurs when two or more mics pick up sound from the same audio source. Because the sounds arrive at the mic at slightly different times, they end up being out of phase and to various degrees cancel each other out.

When multiple mics are used on a set there are four things you can do to reduce or eliminate the resulting phase cancellation:

• place mics as close as possible to sound sources  
• use directional mics 
• turn down mics any time they are not needed 
• carefully check and vary distances between the sound sources and multiple mics to reduce or eliminate any cancellation effect (A speaker's mic should be placed at one-third or less the distance of the next nearest mic.)

In the next section we'll explore another dimension of audio: stereo and surround-sound.