Back porch

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Portion of a PAL videosignal. From left to right: end of a video scan line, front porch, horizontal sync pulse, back porch with color burst, and beginning of next line

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 is used to restore the black level reference in analog video. In signal processing terms, it compensates for the fall time and settling time following the sync pulse.

• In color TV systems such as PAL and NTSC, this period also includes the colorburst signal. In the SECAM system it contains the reference subcarrier for each consecutive color difference signal in order to set the zero-color reference.
• 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.

See also

• Front porch
• Sync pulse
• Horizontal blanking interval
• Vertical blanking interval
• Porch (as in buildings)