Interruptible foldback, also known as interruptible feedback, interrupted feedback, and interrupted foldback, abbreviated IFB, is a monitoring and cueing system used in television, filmmaking, video production, and radio broadcast for one-way communication from the director or assistant director to on-air talent or a remote location. Less common names for the system include program cue interrupt (PI), switched talkback and interrupt for broadcast.
The IFB is a special intercom circuit that consists of a mix-minus program feed sent to an earpiece worn by talent via a wire, telephone, or radio receiver (audio that is being "fed back" to talent) that can be interrupted and replaced by a television producer's or director's intercom microphone. On a television news program for example, a producer can talk to the news anchors, to tell them when they are live on the air and when to begin reading off the script on the teleprompter or cue cards.
In electronic news gathering (ENG), the IFB can be sent through a telephone hybrid, or some other return link in a broadcast auxiliary service. Because of the physics of electronics, all signals will suffer a time delay as they travel through a wire, or during the conversion to radio frequency and then back to electronic audio, or in the conversion from analogue to digital signal and back again to the analogue realm. To achieve the mix-minus program to the IFB, certain audio elements that originate remotely from the mix point will be eliminated from the mix sent back to the remote site to avoid an undesirable echo.
Wired or wireless in-ear monitors (IEMs) may be used to carry the IFB audio to the on-air talent.
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