 Analogue video signals contain a frequency content from 25 Hz up to around 5 MHz, and so variations in frequency responses will affect the picture in various ways, depending on whether it is high frequency (>1 MHz) or low frequency (<1 MHz) distortion.Low frequency distortion will cause field-rate impairment, manifesting itself as luminance variation between the top and bottom of a picture.High frequency distortion causes problems with sharpness of the picture