Photo of an analog VSYNC signal


Games and graphics card often have a VSYNC ON or VSYNC OFF setting.  But have you ever wondered where VSYNC comes from?  It stands for Vertical Synchronization. From the video signal perspective, it is a signal to the display to begin a new refresh cycle.

This is the vertical blanking interval. It allows displays to synchronize to the next refresh cycle. We used to see it on analog TVs in 1930s through 1980s when the picture rolled during lost sync. Known as vertical synchronization, aka VSYNC (it is also padded with Front Porch and Back Porch) This hidden sync signal still exists in digital signals, DVI, HDMI, DisplayPort, and is seen on PCs and Macs via Custom Resolution Utilities.

If you grew up in the days of old analog TVs in the 1970s/1980s, you may remember that black bar in a rolling picture — from a misadjusted VHOLD setting.

Here’s a picture of the analog version of VSYNC, used by TVs since the 1930s!

Advanced users: See Custom Resolution Utility Glossary