Back porch

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Back porch refers to the portion in each scan line of a video signal between the end (rising edge) of the horizontal sync pulse and the start of active video. It was originally allocated to allow the slow electronics in early televisions time to respond to the sync pulse and prepare for the active line period.

With faster electronics making the delay unnecessary, the period has found other uses:

• In color TV systems such as PAL and NTSC, this period includes the colorburst signal.
• In some professional systems, particularly satellite links between locations, the audio is embedded within the back porch of the video signal, to save the cost of renting a second channel.

[edit] See also

• Front porch
• Vertical blanking interval