A drop-out compensator is an error concealment device that was commonly used in the

analog video Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) syst ...

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

videotape Videotape is magnetic tape used for storing video and usually sound in addition. Information stored can be in the form of either an analog or digital signal. Videotape is used in both video tape recorders (VTRs) and, more commonly, videocasse ...

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 Dedicated drop-out compensators were eventually superseded by the incorporation of drop-out compensation functionality into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 ...

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, an error correction code, sometimes error correcting code, (ECC) is used for controlling errors in data over unreliable or noisy communication channels. The central idea is ...

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.Kur ...

in packetized video transmission, modern error concealment 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 History of television {{tv-tech-stub