2-pop

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Used in television and film post-production, a 2-pop is a 1 kHz tone that is one frame long and placed 2 seconds before the start of program. For example, if program video starts at the typical timecode of 01:00:00:00, then 1 frame of 1 kHz tone at timecode 00:59:58:00 would be placed to create a 2-pop. Typically, in film, the 2-pop is placed at 01:00:06:00.

Whereas laying down bars and tone prior to program start establishes video and audio calibration levels on the tape , the 2-pop is primarily used for picture and sound synchronization. Therefore, while the loudness of the 2-pop may be the same as the bars and tone audio level in use, this is not a requirement. The loudness level should be suffient to be heard clearly.

Associated at the same point in the timeline with the audible 2-pop is a visual flash-frame. Together, the 2-pop and the flash-frame, are used to synchronize the audio and video tracks when more convenient methods are unavailable. Although not typically used in modern NLE outputs, a 2-pop may still be used on a digital output when there is an expectation that the media might be later transferred to a format where a manual sync point would be useful. This is similar in function to the way a film clapperboard is used to synchronize audio and visual footage.