just as the modulation and demodulation of rf degrades quality, the combining of component signals to form the composite signal does the same, causing a checkerboard video artifact known as dot crawl. dot crawl is a defect that results from crosstalk due to the intermodulation of the chrominance and luminance components of the signal. this is usually seen when chrominance is transmitted with high bandwidth, and its spectrum reaches into the band of the luminance frequencies. comb filters are commonly used to separate signals and eliminate these artifacts from composite sources. s-video and component video avoid this problem as they maintain the component signals separately.