A drop-out compensator is an

error concealment Error concealment is a technique used in signal processing that aims to minimize the deterioration of signals caused by missing data, called packet loss. A signal is a message sent from a transmitter to a Receiver (radio), receiver in multiple small ...

device that was commonly used in the

analog video Video is an Electronics, electronic medium for the recording, copying, playback, broadcasting, and display of moving picture, moving image, visual Media (communication), media. Video was first developed for mechanical television systems, whi ...

era to hide brief RF signal ''drop-outs'' on

videotape Videotape is magnetic tape used for storing video and usually Sound recording and reproduction, sound in addition. Information stored can be in the form of either an analog signal, analog or Digital signal (signal processing), digital signal. V ...

playback caused by imperfections in or damage to the tape's magnetic coating. Most compensators worked by repeating earlier video scan lines over short periods of signal loss; one early such system, Mincom, was developed in the 1960s by the Minnesota Mining and Manufacturing Company, the company now known as 3M. Because of the high cost of the 3M device at the time, BBC R&D engineers developed a simpler, less expensive unit based on a

sample-and-hold In electronics, a sample and hold (also known as sample and follow) circuit is an analog device that samples (captures, takes) the voltage of a continuously varying analog signal and holds (locks, freezes) its value at a constant level for a ...

technique for in-house use. Dedicated drop-out compensators were eventually superseded by the incorporation of drop-out compensation functionality into

timebase corrector Time base correction (TBC) is a technique to reduce or eliminate errors caused by mechanical instability present in analog recordings on mechanical media. Without time base correction, a signal from a videotape recorder (VTR) or videocassette re ...

s based on analog-to-digital conversion and digital line stores. The advent of compressed digital video systems finally eliminated the need for line-based drop-out compensators. Most low-level media errors, such as those caused by tape damage or imperfections, are now dealt with by

forward error correction In computing, telecommunication, information theory, and coding theory, forward error correction (FEC) or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels. The centra ...

techniques, and those which overwhelm the FEC layer are typically too severe to remedy using simple line-based error concealment techniques because damage to the compressed bitstream will often damage large parts of the video image. However, since occasional signal drop-outs can still occur, either through severe tape damage or because of

packet loss Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is either caused by errors in data transmission, typically across wireless networks, or network congestion.Ku ...

in packetized video transmission, modern

techniques that are aware of the structure of the compressed video format have been developed to deal with these.

References

Broadcast engineering Error detection and correction Video storage Television technology {{tv-tech-stub