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
See also
*
Packet loss concealment
Packet loss concealment (PLC) is a technique to mask the effects of packet loss in voice over IP (VoIP) communications. When the voice signal is sent as VoIP packets on an IP network, the packets may (and likely will) travel different routes. A pa ...
References
{{reflist
Error
Signal processing
Film and video technology
Audio engineering
Broadcast engineering
Error detection and correction
Film and video terminology