The “2-pop” is the last number on the SMPTE countdown banner, which runs unseen before a reel of a motion picture, television show or commercial starts. Though they generally run unseen, we’ve all seen them before as the banner is sometimes used for creative effect. It looks like an analog clock (complete with a rotating hand) with huge numbers on top of it counting down… 5, 4, 3, 2. The number 1 is never shown because that is when the video or film goes to black so it can be cued up without a number showing up. At the time of the 2 in the countdown there is one frame of a 1000 Hz (or sometimes 400 Hz) tone. One frame isn’t very long so this tone sounds more like a “pop,” hence the name 2-pop. The purpose of this is to verify that audio and video/film are in sync with one another.