Chapter 5 STANDARD-DEFINITION VIDEO FUNDAMENTALS 121 Subcarrier Synchronization (Composite Video Only) In addition to the syncronization signals in the vertical inter- val, the NTSC and PAL composite video formats contain a phase synchronization structure for the color subcarrier. This structure is four fields long in NTSC and eight fields long in PAL. This rela- tionship is referred to as SCH or subcarrier-to-horizontal phase. Editing in a pure-composite environment required editors to maintain the SCH alignment of these four- or eight-field struc- tures or color errors could occur. Fortunately, this is not neces- sary in component video formats as the chroma signal is not contained in a modulated subcarrier. Introduction to Digital Video As we learned earlier in this chapter, sampling is the funda- mental process of creating a video signal by converting what the camera sees into a series of voltages. Though these analog volt- ages can accurately represent the image, there are many prob- lems with analog recordings. Any analog signal is subject to