It’s not uncommon in television facilities to have difficult-to-diagnose audio issues involving microphones. Apart from common problems such as broken wires, popping, and noise, acoustic phase interference can create some very unique issues.
The first type of acoustic phase problem arises when the same sound reaches two or more microphones at different times. A common example of this type of interference can be witnessed when two or more talent are in very close proximity and when one voice is dominant and the other is softer (and thus requires more gain). The 3:1 rule can be used to reduce these problems. Basically, no microphone should be closer to another microphone than three times the distance of the subject. If a lav microphone is 12 inches from the subject’s mouth, then the next closest microphone should be no closer than 36 inches. That situation is more common than you may think, as consultants often have anchors sit very close together behind the anchor desk.
Acoustic phase problems can also occur when just one microphone is employed. If a microphone is placed on a table or podium using a microphone stand, a sound reflection may cause phase interference if the level is within 9 dB of the originating sound. Moving or pointing the microphone away from the reflective surface can improve performance. Often, moving the microphone closer to the subject can solve the problem not just by helping achieve the 9 dB difference, but also there is likely to be less reflective surface as the microphone approaches the rear of the tabletop. Finally, just placing the microphone on the tabletop will help ensure that all sound arrives at the microphone element at the same time.
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