Error concealment is a technique used in

signal processing Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing ''signals'', such as sound, images, and scientific measurements. Signal processing techniques are used to optimize transmissions, ...

that aims to minimize the deterioration of signals caused by missing data, called

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 ...

. A signal is a message sent from a

transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...

to a receiver in multiple small packets. Packet loss occurs when these packets are misdirected, delayed, resequenced, or corrupted.

Receiver-Based Techniques

When error recovery occurs at the receiving end of the signal, it is receiver-based. These techniques focus on correcting corrupted or missing data.

Waveform substitution

Preliminary attempts at receiver-based error concealment involved packet repetition, replacing lost packets with copies of previously received packets. This function is computationally simple and is performed by a device on the receiver end called a "

drop-out compensator A drop-out compensator is an error concealment device that was commonly used in the analog video era to hide brief RF signal "drop-outs" on videotape playback caused by imperfections in or damage to the tape's magnetic coating. Most compensators wo ...

Zero Insertion

When this technique is used, if a packet is lost, its entries are replaced with 0s.

Interpolation

Interpolation involves making educated guesses about the nature of a missing packet. For example, by following speech patterns in audio or

faces The face is the front of an animal's head that features the eyes, nose and mouth, and through which animals express many of their emotions. The face is crucial for human identity, and damage such as scarring or developmental deformities may affe ...

in video.

Buffer

Data buffer In computer science, a data buffer (or just buffer) is a region of a memory used to temporarily store data while it is being moved from one place to another. Typically, the data is stored in a buffer as it is retrieved from an input device (such a ...

s are used for temporarily storing data while waiting for delayed packets to arrive. They are common in internet browser loading bars and video applications, like YouTube.

Transmitter-Based Techniques

Rather than attempting to recover lost packets, other techniques involve anticipating data loss, manipulating the data prior to transmission.

Retransmission

The simplest transmitter-based technique is retransmission, sending the message multiple times. Although this idea is simple, because of the extra time required to send multiple signals, this technique is incapable of supporting real-time applications.

Packet Repetition

Packet repetition, also called forward error correction (FEC), adds redundant data, which the receiver can use to recover lost packets. This minimizes loss, but increases the size of the packet.

Interleaving

Interleaving involves scrambling the data before transmission. When a packet is lost, rather than losing an entire set of data, small portions of several sets will be gone. At the receiving end, the message is then deinterleaved to reveal the original message with minimal loss. Transmission without interleaving: Original transmitted sentence: ThisIsNotAnExampleOfInterleaving Received sentence with a burst error: ThisIsNot______pleOfInterleaving The term "AnExample" ends up mostly unintelligible and difficult to correct. With interleaving: Transmitted sentence: ThisIsAnExampleOfInterleaving... Error-free transmission: TIEpfeaghsxlIrv.iAaenli.snmOten. Received sentence with a burst error: TIEpfe______Irv.iAaenli.snmOten. Received sentence after deinterleaving: T_isI_AnE_amp_eOfInterle_vin_... No word is completely lost and the missing letters can be recovered with minimal guesswork. Forward error correction#Example

Applications

Depending on the method of transmission (analog or digital), there are a variety of ways for errors to propagate in the message.

Analog Applications

Since its invention in the 1950s, the magnetic coating used in

analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analog ...

video tape 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, videocassett ...

has experienced radio frequency (RF) signal drop-outs. Some of the techniques that were used for resolving these issues are analogous to those used for concealing errors in modern compressed video signals. The process of click removal in

audio restoration Audio restoration is the process of removing imperfections (such as hiss, impulse noise, crackle, wow and flutter, background noise, and mains hum) from sound recordings. Audio restoration can be performed directly on the recording medium (f ...

is another example of error concealment. A closely analogous example in the domain of image processing is the use of digital dust and scratch removal processing in film restoration.

Digital Applications

Error concealment has many digital applications, including web browsing, video conferencing, Skype, and YouTube

References

{{reflist Error Signal processing Film and video technology Audio engineering Broadcast engineering Error detection and correction Film and video terminology