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In electronics, crosstalk (XT) is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or channel, to another.
Crosstalk in cabling 
- Near end crosstalk (NEXT)
- Interference between two pairs in a cable measured at the same end of the cable as the interfering transmitter.
- Power sum near end crosstalk (PSNEXT)
- A NEXT measurement which includes the sum of crosstalk contributions of all adjacent pairs.
- Far end crosstalk (FEXT)
- Interference between two pairs of a cable measured at the other end of the cable with respect to the interfering transmitter.
- Equal level far end crosstalk (ELFEXT)
- An FEXT measurement with attenuation compensation.
- Alien crosstalk (AXT)
- Interference caused by other cables routed close to the cable of interest.
Other examples 
In telecommunication or telephony, crosstalk is often distinguishable as pieces of speech or signaling tones leaking from other people's connections. If the connection is analog, twisted pair cabling can often be used to reduce the effects of crosstalk. Alternatively, the signals can be converted to digital form, which is much less susceptible to crosstalk.
In integrated circuit design, crosstalk normally refers to a signal affecting another nearby signal. Usually the coupling is capacitive, and to the nearest neighbor, but other forms of coupling and effects on signal further away are sometimes important, especially in analog designs. See signal integrity for tools used to measure and prevent this problem, and substrate coupling for a discussion of crosstalk conveyed through the integrated circuit substrate. There are a wide variety of possible fixes, with increased spacing, wire re-ordering, and shielding being the most common.
In full-field optical coherence tomography, "crosstalk" refers to the phenomenon that due to highly scattering objects, multiple scattered photons reach the image plane and generate coherent signal after traveling a pathlength that matches that of the sample depth within a coherence length.
In stereoscopic 3D displays, "crosstalk" refers to the incomplete isolation of the left and right image channels so that one leaks or bleeds into the other - like a double exposure, which produces a ghosting effect.
See also 
- Attenuation-to-crosstalk ratio
- Audio system measurements
- Co-channel interference (CCI)
- Federal Standard 1037C
- Signal integrity
- Signal-to-interference ratio (SIR or S/I), also known as carrier-to-interference ratio (CIR or C/I)
- Substrate coupling
- Unger model
- "Category 5 / 5E & Cat 6 Cabling Tutorial and FAQ's". lanshack.com. Retrieved 2013-01-05.
- Eliminating alien crosstalk, Communications News, February 2009, archived from the original on 2012-02-09
- Federal Standard 1037C glossary Archived 2011-10-24.