On an empty channel, an analog TV receiver shows a "snowy" noise pattern. A similar pattern is shown if on a digital channel when not using a DTV converter box.

An old black and white receiver showing noise.

Noise in analog video and television is perceived as a random dot pattern which is superimposed on the picture as a result of electronic noise and radiated electromagnetic noise picked up by the receiver's antenna—it is the "snow" which is seen with poor analog television reception or on VHS tapes.

When there is no transmission, which is to say no signal, the noise or "snow" is due mostly to thermal noise from the device itself, stray electromagnetic fields from other household electric devices, and other electromagnetic signals, all of which is interpreted as luminance signal. Most of this noise comes from the first transistor the antenna is attached to.^[1]

Due to the algorithmic functioning of a digital television set's electronic circuitry and the inherent quantization of its screen, the "snow" seen on digital TV is less random.^[2]

UK viewers used to see "snow" on black after sign-off, instead of "bugs" on white, a purely technical artifact due to old 405-line British receivers using positive rather than the negative video modulation used in Canada, the U.S., and (currently) the UK as well.

Since one impression of the "snow" is of fast-flickering black bugs on a cool white background, in Sweden, Denmark and Hungary the phenomenon is often called Myrornas krig in Swedish, Myrekrig in Danish and "Hangyák háborúja" in Hungarian, which translate to "War of the Ants" and "Ant war".^[3]

[edit] References

[edit] See also

• Noise (radio)
• Interference (wave propagation)

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